From 49b0ab0e1f7d96e58ffe474c32bba60e16f19201 Mon Sep 17 00:00:00 2001
From: Pranav <pranav@chatwoot.com>
Date: Thu, 2 Jul 2026 01:03:22 -0700
Subject: [PATCH] fix: Consider business hours when computing SLA breaches
 (#13392)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- Fixes SLA breach computation to respect the "Only during business
hours" setting
- Backend now pre-computes SLA deadlines, simplifying frontend logic

## How it works

Before: SLA deadlines were calculated using wall-clock time, ignoring
business hours.

After: When an SLA policy has "Only during business hours" enabled and
the inbox has working hours configured, the deadline is calculated by
adding threshold time only during business hours.


**How you check if a conversation has a SLA hit or miss?**

<img width="474" height="510" alt="Screenshot 2026-01-28 at 7 06 53 PM"
src="https://github.com/user-attachments/assets/54ec8581-18b8-45c6-a356-de8c778ea78d"
/>


**Example:**
- Conversation created: Friday 4:30 PM
- FRT threshold: 1 hour
- Business hours: Mon-Fri 9 AM - 5 PM

| | Breach time |
|--|--|
| Before | Friday 5:30 PM |
| After | Monday 9:30 AM |

## Test plan

- [x] Create an SLA policy with "Only during business hours" enabled
- [x] Configure inbox with business hours (e.g., Mon-Fri 9-5)
- [x] Conversation created during business hours
  - Create a conversation on Wednesday 10:00 AM UTC
- Expected: FRT deadline shows Wednesday 12:00 PM UTC (2 business hours
later)
- [x] Conversation created before business hours
  - Create a conversation on Wednesday 7:00 AM UTC
- Expected: FRT deadline shows Wednesday 11:00 AM UTC (counting starts
at 9 AM)
- [x] Conversation created after business hours
  - Create a conversation on Wednesday 6:00 PM UTC
- Expected: FRT deadline shows Thursday 11:00 AM UTC (counting starts
next day 9 AM)
- [x] Conversation created on weekend
  - Create a conversation on Saturday 10:00 AM UTC
  - Expected: FRT deadline shows Monday 11:00 AM UTC (skips weekend)
- [x] Threshold spans weekend
  - Create a conversation on Friday 4:00 PM UTC with 2-hour FRT
- Expected: FRT deadline shows Monday 10:00 AM UTC (1h Friday + 1h
Monday)
- [x] SLA without business hours
  - Create an SLA policy with only_during_business_hours: false
  - Create a conversation on Friday 4:00 PM UTC with 2-hour FRT
  - Expected: FRT deadline shows Friday 6:00 PM UTC (wall-clock time)
- [x] All Day marked as closed_all_day
  - Create a conversation on Tuesday 4:00 PM UTC with 2-hour FRT
  - Expected: FRT deadline shows Thursday 10:00 AM UTC
- [x] All Day marked as open_all_day
  - Create a conversation on Saturday 10:00 AM UTC with 2-hour FRT
  - Expected: FRT deadline shows Saturday 12:00 PM UTC
- [x] UI displays correct countdown
  - Verify conversation card shows correct SLA timer
  - Verify timer shows flame icon when breached
  - Verify timer shows alarm icon when within threshold
  - Time updates automatically when time passes
- [x] Verify the breach with a different timezone than your local
timezone

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Sony Mathew <sony@chatwoot.com>
Co-authored-by: Sony Mathew <2040199+sony-mathew@users.noreply.github.com>
---
 .../ConversationCard/SLACardLabel.vue         |  15 +-
 .../Conversation/Sla/SLACardLabel.vue         |   4 +-
 .../conversation/components/SLACardLabel.vue  |   3 +-
 app/javascript/dashboard/helper/slaHelper.js  | 150 ++++++
 .../dashboard/helper/specs/slaHelper.spec.js  | 450 ++++++++++++++++++
 .../finders/enterprise/conversation_finder.rb |   4 +-
 enterprise/app/models/applied_sla.rb          |  59 ++-
 .../services/sla/business_hours_service.rb    | 108 +++++
 .../sla/evaluate_applied_sla_service.rb       | 155 +++---
 .../api/v1/models/_applied_sla.json.jbuilder  |   4 +
 spec/enterprise/models/applied_sla_spec.rb    | 119 ++++-
 .../sla/business_hours_service_spec.rb        | 184 +++++++
 .../sla/evaluate_applied_sla_service_spec.rb  |  73 ++-
 13 files changed, 1228 insertions(+), 100 deletions(-)
 create mode 100644 app/javascript/dashboard/helper/slaHelper.js
 create mode 100644 app/javascript/dashboard/helper/specs/slaHelper.spec.js
 create mode 100644 enterprise/app/services/sla/business_hours_service.rb
 create mode 100644 spec/enterprise/services/sla/business_hours_service_spec.rb

diff --git a/app/javascript/dashboard/components-next/Conversation/ConversationCard/SLACardLabel.vue b/app/javascript/dashboard/components-next/Conversation/ConversationCard/SLACardLabel.vue
index ff57d6c93..608bd84bd 100644
--- a/app/javascript/dashboard/components-next/Conversation/ConversationCard/SLACardLabel.vue
+++ b/app/javascript/dashboard/components-next/Conversation/ConversationCard/SLACardLabel.vue
@@ -1,6 +1,6 @@
 <script setup>
 import { ref, computed, onMounted, onUnmounted, watch } from 'vue';
-import { evaluateSLAStatus } from '@chatwoot/utils';
+import { evaluateSLAStatus } from 'dashboard/helper/slaHelper';
 
 const props = defineProps({
   conversation: {
@@ -19,16 +19,8 @@ const slaStatus = ref({
   icon: null,
 });
 
-// TODO: Remove this once we update the helper from utils
-// https://github.com/chatwoot/utils/blob/main/src/sla.ts#L73
-const convertObjectCamelCaseToSnakeCase = object => {
-  return Object.keys(object).reduce((acc, key) => {
-    acc[key.replace(/([A-Z])/g, '_$1').toLowerCase()] = object[key];
-    return acc;
-  }, {});
-};
-
 const appliedSLA = computed(() => props.conversation?.appliedSla);
+const slaEvents = computed(() => props.conversation?.slaEvents);
 const isSlaMissed = computed(() => slaStatus.value?.isSlaMissed);
 
 const hasSlaThreshold = computed(() => {
@@ -41,8 +33,9 @@ const slaStatusText = computed(() => {
 
 const updateSlaStatus = () => {
   slaStatus.value = evaluateSLAStatus({
-    appliedSla: convertObjectCamelCaseToSnakeCase(appliedSLA.value || {}),
+    appliedSla: appliedSLA.value || {},
     chat: props.conversation,
+    slaEvents: slaEvents.value || [],
   });
 };
 
diff --git a/app/javascript/dashboard/components-next/Conversation/Sla/SLACardLabel.vue b/app/javascript/dashboard/components-next/Conversation/Sla/SLACardLabel.vue
index 98a79c921..359e237ec 100644
--- a/app/javascript/dashboard/components-next/Conversation/Sla/SLACardLabel.vue
+++ b/app/javascript/dashboard/components-next/Conversation/Sla/SLACardLabel.vue
@@ -1,6 +1,6 @@
 <script setup>
 import { ref, computed, onMounted, onUnmounted, watch } from 'vue';
-import { evaluateSLAStatus } from '@chatwoot/utils';
+import { evaluateSLAStatus } from 'dashboard/helper/slaHelper';
 
 import Icon from 'dashboard/components-next/icon/Icon.vue';
 import Label from 'dashboard/components-next/label/Label.vue';
@@ -27,6 +27,7 @@ defineOptions({
 });
 
 const appliedSLA = computed(() => props.chat?.applied_sla);
+const slaEvents = computed(() => props.chat?.sla_events);
 const hasSlaThreshold = computed(() => slaStatus.value?.threshold);
 const isSlaMissed = computed(() => slaStatus.value?.isSlaMissed);
 
@@ -34,6 +35,7 @@ const updateSlaStatus = () => {
   slaStatus.value = evaluateSLAStatus({
     appliedSla: appliedSLA.value || {},
     chat: props.chat,
+    slaEvents: slaEvents.value || [],
   });
 };
 
diff --git a/app/javascript/dashboard/components/widgets/conversation/components/SLACardLabel.vue b/app/javascript/dashboard/components/widgets/conversation/components/SLACardLabel.vue
index bb6ee48d2..f5e2d4522 100644
--- a/app/javascript/dashboard/components/widgets/conversation/components/SLACardLabel.vue
+++ b/app/javascript/dashboard/components/widgets/conversation/components/SLACardLabel.vue
@@ -1,7 +1,7 @@
 <script setup>
 import { ref, computed, onMounted, onUnmounted, watch } from 'vue';
 import { useI18n } from 'vue-i18n';
-import { evaluateSLAStatus } from '@chatwoot/utils';
+import { evaluateSLAStatus } from 'dashboard/helper/slaHelper';
 import SLAPopoverCard from './SLAPopoverCard.vue';
 
 const props = defineProps({
@@ -61,6 +61,7 @@ const updateSlaStatus = () => {
   slaStatus.value = evaluateSLAStatus({
     appliedSla: appliedSLA.value,
     chat: props.chat,
+    slaEvents: slaEvents.value || [],
   });
 };
 
diff --git a/app/javascript/dashboard/helper/slaHelper.js b/app/javascript/dashboard/helper/slaHelper.js
new file mode 100644
index 000000000..9c69f9d0b
--- /dev/null
+++ b/app/javascript/dashboard/helper/slaHelper.js
@@ -0,0 +1,150 @@
+import { useCamelCase } from 'dashboard/composables/useTransformKeys';
+
+/**
+ * Formats seconds into a human-readable time string
+ * @param {number} seconds - The time in seconds (can be negative for overdue)
+ * @returns {string} Formatted time string like "2h 30m" or "1d 4h"
+ */
+const formatSLATime = seconds => {
+  const absSeconds = Math.abs(seconds);
+
+  const units = {
+    y: 31536000,
+    mo: 2592000,
+    d: 86400,
+    h: 3600,
+    m: 60,
+  };
+
+  if (absSeconds < 60) {
+    return '1m';
+  }
+
+  const parts = [];
+  let remaining = absSeconds;
+
+  Object.entries(units).forEach(([unit, value]) => {
+    if (parts.length >= 2) return;
+    const count = Math.floor(remaining / value);
+    if (count > 0) {
+      parts.push(`${count}${unit}`);
+      remaining -= count * value;
+    }
+  });
+
+  return parts.join(' ');
+};
+
+const toUnixTimestamp = value => {
+  if (!value || typeof value === 'number') return value;
+
+  const numericValue = Number(value);
+  if (!Number.isNaN(numericValue)) return numericValue;
+
+  const parsedTimestamp = Date.parse(value);
+  return Number.isNaN(parsedTimestamp)
+    ? value
+    : Math.floor(parsedTimestamp / 1000);
+};
+
+/**
+ * Evaluates SLA status using backend-computed due times
+ * @param {Object} params - Parameters object
+ * @param {Object} params.appliedSla - The applied SLA with due_at timestamps
+ * @param {Object} params.chat - The conversation object
+ * @param {Array} params.slaEvents - Recorded SLA miss events for this conversation
+ * @returns {Object} SLA status with type, threshold, icon, and isSlaMissed
+ */
+export const evaluateSLAStatus = ({ appliedSla, chat, slaEvents = [] }) => {
+  const emptyStatus = { type: '', threshold: '', icon: '', isSlaMissed: false };
+
+  if (!appliedSla || !chat) {
+    return emptyStatus;
+  }
+
+  const sla = useCamelCase(appliedSla);
+  const conversation = useCamelCase(chat);
+  const events = useCamelCase(slaEvents || []);
+  const currentTime = Math.floor(Date.now() / 1000);
+  const slaStatuses = [];
+
+  const dueAtByType = {
+    FRT: sla.slaFrtDueAt,
+    RT: sla.slaRtDueAt,
+  };
+  const slaTypes = ['FRT', 'NRT', 'RT'];
+
+  events.forEach(event => {
+    const type = event.eventType?.toUpperCase();
+    if (!slaTypes.includes(type)) return;
+
+    const missedAt =
+      type === 'NRT' ? event.createdAt : dueAtByType[type] || event.createdAt;
+    if (!missedAt) return;
+
+    slaStatuses.push({
+      type,
+      threshold: missedAt - currentTime,
+      icon: 'flame',
+      isSlaMissed: true,
+    });
+  });
+
+  const firstReplyCreatedAt = toUnixTimestamp(conversation.firstReplyCreatedAt);
+  const shouldCheckFirstResponse =
+    !firstReplyCreatedAt || firstReplyCreatedAt > sla.slaFrtDueAt;
+
+  // Check FRT - until first reply is made on time
+  if (sla.slaFrtDueAt && shouldCheckFirstResponse) {
+    const threshold = sla.slaFrtDueAt - currentTime;
+    slaStatuses.push({
+      type: 'FRT',
+      threshold,
+      icon: threshold <= 0 ? 'flame' : 'alarm',
+      isSlaMissed: threshold <= 0,
+    });
+  }
+
+  // Check NRT - only if first reply made and waiting for response
+  if (sla.slaNrtDueAt && firstReplyCreatedAt && conversation.waitingSince) {
+    const threshold = sla.slaNrtDueAt - currentTime;
+    slaStatuses.push({
+      type: 'NRT',
+      threshold,
+      icon: threshold <= 0 ? 'flame' : 'alarm',
+      isSlaMissed: threshold <= 0,
+    });
+  }
+
+  // Check RT - only if conversation is unresolved
+  if (sla.slaRtDueAt && conversation.status !== 'resolved') {
+    const threshold = sla.slaRtDueAt - currentTime;
+    slaStatuses.push({
+      type: 'RT',
+      threshold,
+      icon: threshold <= 0 ? 'flame' : 'alarm',
+      isSlaMissed: threshold <= 0,
+    });
+  }
+
+  if (slaStatuses.length === 0) {
+    return emptyStatus;
+  }
+
+  // Show existing breaches before upcoming deadlines, then pick the closest timer.
+  slaStatuses.sort((a, b) => {
+    if (a.isSlaMissed !== b.isSlaMissed) {
+      return a.isSlaMissed ? -1 : 1;
+    }
+
+    return Math.abs(a.threshold) - Math.abs(b.threshold);
+  });
+  const mostUrgent = slaStatuses[0];
+
+  return {
+    type: mostUrgent.type,
+    threshold: formatSLATime(mostUrgent.threshold),
+    icon: mostUrgent.icon,
+    isSlaMissed: mostUrgent.isSlaMissed,
+  };
+};
diff --git a/app/javascript/dashboard/helper/specs/slaHelper.spec.js b/app/javascript/dashboard/helper/specs/slaHelper.spec.js
new file mode 100644
index 000000000..466112f7d
--- /dev/null
+++ b/app/javascript/dashboard/helper/specs/slaHelper.spec.js
@@ -0,0 +1,450 @@
+import { evaluateSLAStatus } from '../slaHelper';
+
+describe('#SLA Helpers', () => {
+  const currentTimestamp = 1700000000; // Fixed timestamp for testing
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.setSystemTime(currentTimestamp * 1000);
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  describe('evaluateSLAStatus', () => {
+    describe('when inputs are invalid', () => {
+      it('returns empty status when appliedSla is null', () => {
+        const result = evaluateSLAStatus({ appliedSla: null, chat: {} });
+        expect(result).toEqual({
+          type: '',
+          threshold: '',
+          icon: '',
+          isSlaMissed: false,
+        });
+      });
+
+      it('returns empty status when chat is null', () => {
+        const result = evaluateSLAStatus({ appliedSla: {}, chat: null });
+        expect(result).toEqual({
+          type: '',
+          threshold: '',
+          icon: '',
+          isSlaMissed: false,
+        });
+      });
+    });
+
+    describe('FRT (First Response Time)', () => {
+      it('returns FRT status when first reply not made and within threshold', () => {
+        const appliedSla = { sla_frt_due_at: currentTimestamp + 3600 }; // 1 hour from now
+        const chat = { first_reply_created_at: null, status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('1h');
+        expect(result.icon).toBe('alarm');
+        expect(result.isSlaMissed).toBe(false);
+      });
+
+      it('returns missed FRT status when threshold is exceeded', () => {
+        const appliedSla = { sla_frt_due_at: currentTimestamp - 1800 }; // 30 min ago
+        const chat = { first_reply_created_at: null, status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('30m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('does not return FRT when first reply was made before due time', () => {
+        const appliedSla = { sla_frt_due_at: currentTimestamp + 3600 };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 1000,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).not.toBe('FRT');
+      });
+
+      it('does not return FRT when first reply was made at due time', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp - 600,
+          sla_rt_due_at: currentTimestamp + 1800,
+        };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 600,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('RT');
+      });
+
+      it('returns missed FRT when first reply was made after due time', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp - 600,
+          sla_rt_due_at: currentTimestamp + 1800,
+        };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 300,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('10m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('returns missed FRT when live first reply timestamp is an ISO string after due time', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp - 600,
+          sla_rt_due_at: currentTimestamp + 1800,
+        };
+        const chat = {
+          first_reply_created_at: new Date(
+            (currentTimestamp - 300) * 1000
+          ).toISOString(),
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('10m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('uses the due time for a missed FRT event created after the deadline', () => {
+        const appliedSla = { sla_frt_due_at: currentTimestamp - 3600 };
+        const chat = { first_reply_created_at: null, status: 'open' };
+        const slaEvents = [
+          { event_type: 'frt', created_at: currentTimestamp - 1800 },
+        ];
+
+        const result = evaluateSLAStatus({ appliedSla, chat, slaEvents });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('1h');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+    });
+
+    describe('NRT (Next Response Time)', () => {
+      it('returns NRT status when waiting for response and within threshold', () => {
+        const appliedSla = { sla_nrt_due_at: currentTimestamp + 1800 }; // 30 min from now
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: currentTimestamp - 600,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('NRT');
+        expect(result.threshold).toBe('30m');
+        expect(result.icon).toBe('alarm');
+        expect(result.isSlaMissed).toBe(false);
+      });
+
+      it('returns missed NRT status when threshold is exceeded', () => {
+        const appliedSla = { sla_nrt_due_at: currentTimestamp - 900 }; // 15 min ago
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: currentTimestamp - 2700,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('NRT');
+        expect(result.threshold).toBe('15m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('does not return NRT when not waiting for response', () => {
+        const appliedSla = { sla_nrt_due_at: currentTimestamp + 1800 };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: null,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).not.toBe('NRT');
+      });
+
+      it('returns missed NRT when a recorded NRT miss exists after response', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp + 1800 };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: null,
+          status: 'open',
+        };
+        const slaEvents = [
+          { event_type: 'nrt', created_at: currentTimestamp - 900 },
+        ];
+
+        const result = evaluateSLAStatus({ appliedSla, chat, slaEvents });
+
+        expect(result.type).toBe('NRT');
+        expect(result.threshold).toBe('15m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('uses the recorded event time for a missed NRT with a new active NRT timer', () => {
+        const appliedSla = {
+          sla_nrt_due_at: currentTimestamp + 300,
+          sla_rt_due_at: currentTimestamp + 1800,
+        };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: currentTimestamp - 60,
+          status: 'open',
+        };
+        const slaEvents = [
+          { event_type: 'nrt', created_at: currentTimestamp - 1800 },
+        ];
+
+        const result = evaluateSLAStatus({ appliedSla, chat, slaEvents });
+
+        expect(result.type).toBe('NRT');
+        expect(result.threshold).toBe('30m');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('does not return NRT when first reply not made', () => {
+        const appliedSla = { sla_nrt_due_at: currentTimestamp + 1800 };
+        const chat = {
+          first_reply_created_at: null,
+          waiting_since: currentTimestamp - 600,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).not.toBe('NRT');
+      });
+    });
+
+    describe('RT (Resolution Time)', () => {
+      it('returns RT status when conversation is open and within threshold', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp + 7200 }; // 2 hours from now
+        const chat = {
+          first_reply_created_at: currentTimestamp - 3600,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('RT');
+        expect(result.threshold).toBe('2h');
+        expect(result.icon).toBe('alarm');
+        expect(result.isSlaMissed).toBe(false);
+      });
+
+      it.each(['pending', 'snoozed'])(
+        'returns RT status when conversation is %s and within threshold',
+        status => {
+          const appliedSla = { sla_rt_due_at: currentTimestamp + 7200 };
+          const chat = {
+            first_reply_created_at: currentTimestamp - 3600,
+            status,
+          };
+
+          const result = evaluateSLAStatus({ appliedSla, chat });
+
+          expect(result.type).toBe('RT');
+          expect(result.threshold).toBe('2h');
+          expect(result.icon).toBe('alarm');
+          expect(result.isSlaMissed).toBe(false);
+        }
+      );
+
+      it('returns missed RT status when threshold is exceeded', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp - 3600 }; // 1 hour ago
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('RT');
+        expect(result.threshold).toBe('1h');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('uses the due time for a missed RT event created after the deadline', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp - 3600 };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          status: 'open',
+        };
+        const slaEvents = [
+          { event_type: 'rt', created_at: currentTimestamp - 1800 },
+        ];
+
+        const result = evaluateSLAStatus({ appliedSla, chat, slaEvents });
+
+        expect(result.type).toBe('RT');
+        expect(result.threshold).toBe('1h');
+        expect(result.icon).toBe('flame');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('does not return RT when conversation is resolved', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp + 7200 };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 3600,
+          status: 'resolved',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('');
+      });
+    });
+
+    describe('priority selection', () => {
+      it('returns most urgent SLA when multiple are active', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp + 7200, // 2h - less urgent
+          sla_nrt_due_at: currentTimestamp + 1800, // 30m - most urgent
+          sla_rt_due_at: currentTimestamp + 3600, // 1h
+        };
+        const chat = {
+          first_reply_created_at: null,
+          waiting_since: currentTimestamp - 600,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        // FRT is selected because first_reply_created_at is null
+        // NRT is not checked when first_reply_created_at is null
+        expect(result.type).toBe('RT');
+        expect(result.threshold).toBe('1h');
+      });
+
+      it('returns most urgent missed SLA over upcoming SLA', () => {
+        const appliedSla = {
+          sla_nrt_due_at: currentTimestamp - 300, // 5m overdue - most urgent by absolute value
+          sla_rt_due_at: currentTimestamp + 3600, // 1h remaining
+        };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 7200,
+          waiting_since: currentTimestamp - 2100,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('NRT');
+        expect(result.isSlaMissed).toBe(true);
+      });
+
+      it('returns an existing missed SLA over a closer upcoming SLA', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp - 7200, // 2h overdue
+          sla_rt_due_at: currentTimestamp + 300, // 5m remaining
+        };
+        const chat = {
+          first_reply_created_at: null,
+          status: 'open',
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.type).toBe('FRT');
+        expect(result.threshold).toBe('2h');
+        expect(result.isSlaMissed).toBe(true);
+      });
+    });
+
+    describe('time formatting', () => {
+      it('formats time in days and hours', () => {
+        const appliedSla = { sla_rt_due_at: currentTimestamp + 90000 }; // 25 hours
+        const chat = { status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.threshold).toBe('1d 1h');
+      });
+
+      it('formats time less than a minute as 1m', () => {
+        const appliedSla = { sla_frt_due_at: currentTimestamp + 30 }; // 30 seconds
+        const chat = { first_reply_created_at: null, status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.threshold).toBe('1m');
+      });
+
+      it('formats months correctly', () => {
+        const appliedSla = {
+          sla_rt_due_at: currentTimestamp + 2592000 + 86400,
+        }; // 1 month + 1 day
+        const chat = { status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result.threshold).toBe('1mo 1d');
+      });
+    });
+
+    describe('empty status scenarios', () => {
+      it('returns empty when no SLA thresholds are set', () => {
+        const appliedSla = {};
+        const chat = { status: 'open' };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result).toEqual({
+          type: '',
+          threshold: '',
+          icon: '',
+          isSlaMissed: false,
+        });
+      });
+
+      it('returns empty when all conditions are met', () => {
+        const appliedSla = {
+          sla_frt_due_at: currentTimestamp + 3600,
+          sla_nrt_due_at: currentTimestamp + 1800,
+          sla_rt_due_at: currentTimestamp + 7200,
+        };
+        const chat = {
+          first_reply_created_at: currentTimestamp - 3600, // FRT already hit
+          waiting_since: null, // Not waiting, so NRT not applicable
+          status: 'resolved', // RT not applicable
+        };
+
+        const result = evaluateSLAStatus({ appliedSla, chat });
+
+        expect(result).toEqual({
+          type: '',
+          threshold: '',
+          icon: '',
+          isSlaMissed: false,
+        });
+      });
+    });
+  });
+});
diff --git a/enterprise/app/finders/enterprise/conversation_finder.rb b/enterprise/app/finders/enterprise/conversation_finder.rb
index 24e6b493d..a28eaf5f9 100644
--- a/enterprise/app/finders/enterprise/conversation_finder.rb
+++ b/enterprise/app/finders/enterprise/conversation_finder.rb
@@ -1,5 +1,7 @@
 module Enterprise::ConversationFinder
   def conversations_base_query
-    current_account.feature_enabled?('sla') ? super.includes(:applied_sla, :sla_events) : super
+    return super unless current_account.feature_enabled?('sla')
+
+    super.includes(:applied_sla, :sla_events, inbox: :working_hours)
   end
 end
diff --git a/enterprise/app/models/applied_sla.rb b/enterprise/app/models/applied_sla.rb
index 112f9deea..092daf256 100644
--- a/enterprise/app/models/applied_sla.rb
+++ b/enterprise/app/models/applied_sla.rb
@@ -44,6 +44,8 @@ class AppliedSla < ApplicationRecord
   after_update_commit :push_conversation_event
 
   def push_event_data
+    sla_due_at_values = due_at_values
+
     {
       id: id,
       sla_id: sla_policy_id,
@@ -55,10 +57,65 @@ class AppliedSla < ApplicationRecord
       sla_first_response_time_threshold: sla_policy.first_response_time_threshold,
       sla_next_response_time_threshold: sla_policy.next_response_time_threshold,
       sla_only_during_business_hours: sla_policy.only_during_business_hours,
-      sla_resolution_time_threshold: sla_policy.resolution_time_threshold
+      sla_resolution_time_threshold: sla_policy.resolution_time_threshold,
+      sla_frt_due_at: sla_due_at_values[:frt],
+      sla_nrt_due_at: sla_due_at_values[:nrt],
+      sla_rt_due_at: sla_due_at_values[:rt]
     }
   end
 
+  def due_at_values
+    working_hours_by_day_cache = conversation.inbox.working_hours.index_by(&:day_of_week) if sla_policy.only_during_business_hours?
+
+    {
+      frt: frt_due_at(working_hours_by_day_cache: working_hours_by_day_cache),
+      nrt: nrt_due_at(working_hours_by_day_cache: working_hours_by_day_cache),
+      rt: rt_due_at(working_hours_by_day_cache: working_hours_by_day_cache)
+    }
+  end
+
+  def frt_due_at(working_hours_by_day_cache: nil)
+    return nil if sla_policy.first_response_time_threshold.blank?
+
+    calculate_due_at(
+      conversation.created_at,
+      sla_policy.first_response_time_threshold,
+      working_hours_by_day_cache: working_hours_by_day_cache
+    )
+  end
+
+  def nrt_due_at(working_hours_by_day_cache: nil)
+    return nil if sla_policy.next_response_time_threshold.blank?
+    return nil if conversation.waiting_since.blank?
+
+    calculate_due_at(
+      conversation.waiting_since,
+      sla_policy.next_response_time_threshold,
+      working_hours_by_day_cache: working_hours_by_day_cache
+    )
+  end
+
+  def rt_due_at(working_hours_by_day_cache: nil)
+    return nil if sla_policy.resolution_time_threshold.blank?
+
+    calculate_due_at(
+      conversation.created_at,
+      sla_policy.resolution_time_threshold,
+      working_hours_by_day_cache: working_hours_by_day_cache
+    )
+  end
+
+  def calculate_due_at(start_time, threshold_seconds, working_hours_by_day_cache: nil)
+    return (start_time + threshold_seconds.to_i.seconds).to_i unless sla_policy.only_during_business_hours?
+
+    Sla::BusinessHoursService.new(
+      inbox: conversation.inbox,
+      start_time: start_time,
+      threshold_seconds: threshold_seconds,
+      working_hours_by_day_cache: working_hours_by_day_cache
+    ).deadline.to_i
+  end
+
   private
 
   def push_conversation_event
diff --git a/enterprise/app/services/sla/business_hours_service.rb b/enterprise/app/services/sla/business_hours_service.rb
new file mode 100644
index 000000000..658738241
--- /dev/null
+++ b/enterprise/app/services/sla/business_hours_service.rb
@@ -0,0 +1,108 @@
+class Sla::BusinessHoursService
+  pattr_initialize [:inbox!, :start_time!, :threshold_seconds!, { working_hours_by_day_cache: nil }]
+
+  def deadline
+    return start_time + threshold_seconds.seconds unless should_apply_business_hours?
+
+    calculate_deadline_with_business_hours
+  end
+
+  private
+
+  def should_apply_business_hours?
+    inbox.working_hours_enabled? && open_days?
+  end
+
+  def open_days?
+    working_hours_by_day.values.any? { |working_hour| !working_hour.closed_all_day? }
+  end
+
+  def calculate_deadline_with_business_hours
+    @remaining_seconds = threshold_seconds.to_i
+    @current_time = start_time.in_time_zone(timezone)
+
+    process_remaining_seconds while @remaining_seconds.positive?
+
+    @current_time
+  end
+
+  def process_remaining_seconds
+    working_hour = working_hour_for(@current_time)
+
+    if closed_day?(working_hour)
+      @current_time = next_business_day_start(@current_time)
+      return
+    end
+
+    # If adjust moved to next day, return early to re-fetch correct working hours
+    return unless adjust_current_time_to_business_hours(working_hour)
+
+    consume_available_seconds(working_hour)
+  end
+
+  def closed_day?(working_hour)
+    working_hour.nil? || working_hour.closed_all_day?
+  end
+
+  # Returns true if current_time was adjusted within the same day, false if moved to next day
+  def adjust_current_time_to_business_hours(working_hour)
+    day_open_time = time_on_date(@current_time, working_hour.open_hour, working_hour.open_minutes)
+    day_close_time = day_close_time_for(working_hour)
+
+    if @current_time < day_open_time
+      @current_time = day_open_time
+      true
+    elsif @current_time >= day_close_time
+      @current_time = next_business_day_start(@current_time)
+      false
+    else
+      true
+    end
+  end
+
+  def consume_available_seconds(working_hour)
+    day_close_time = day_close_time_for(working_hour)
+    available_seconds = (day_close_time - @current_time).to_i
+
+    if @remaining_seconds <= available_seconds
+      @current_time += @remaining_seconds.seconds
+      @remaining_seconds = 0
+    else
+      @remaining_seconds -= available_seconds
+      @current_time = next_business_day_start(@current_time)
+    end
+  end
+
+  def day_close_time_for(working_hour)
+    return @current_time.beginning_of_day + 1.day if working_hour.open_all_day?
+
+    time_on_date(@current_time, working_hour.close_hour, working_hour.close_minutes)
+  end
+
+  def working_hour_for(time)
+    working_hours_by_day[time.wday]
+  end
+
+  def working_hours_by_day
+    @working_hours_by_day ||= working_hours_by_day_cache || inbox.working_hours.index_by(&:day_of_week)
+  end
+
+  def next_business_day_start(current_time)
+    next_day = (current_time + 1.day).beginning_of_day
+    7.times do
+      working_hour = working_hour_for(next_day)
+      return time_on_date(next_day, working_hour.open_hour, working_hour.open_minutes) if working_hour && !working_hour.closed_all_day?
+
+      next_day += 1.day
+    end
+    next_day
+  end
+
+  def time_on_date(date, hour, minutes)
+    date.change(hour: hour, min: minutes, sec: 0)
+  end
+
+  def timezone
+    inbox.timezone || 'UTC'
+  end
+end
diff --git a/enterprise/app/services/sla/evaluate_applied_sla_service.rb b/enterprise/app/services/sla/evaluate_applied_sla_service.rb
index 2da350289..49d01cf93 100644
--- a/enterprise/app/services/sla/evaluate_applied_sla_service.rb
+++ b/enterprise/app/services/sla/evaluate_applied_sla_service.rb
@@ -2,106 +2,101 @@ class Sla::EvaluateAppliedSlaService
   pattr_initialize [:applied_sla!]
 
   def perform
-    check_sla_thresholds
+    check_frt
+    check_nrt
+    check_rt
 
-    # We will calculate again in the next iteration
-    return unless applied_sla.conversation.resolved?
+    return unless conversation.resolved?
 
-    # after conversation is resolved, we will check if the SLA was hit or missed
-    handle_hit_sla(applied_sla)
+    handle_hit_sla
   end
 
   private
 
-  def check_sla_thresholds
-    [:first_response_time_threshold, :next_response_time_threshold, :resolution_time_threshold].each do |threshold|
-      next if applied_sla.sla_policy.send(threshold).blank?
+  delegate :conversation, :sla_policy, to: :applied_sla
 
-      send("check_#{threshold}", applied_sla, applied_sla.conversation, applied_sla.sla_policy)
+  def check_frt
+    return if sla_policy.first_response_time_threshold.blank?
+    return if frt_was_hit?
+    return if within_threshold?(applied_sla.frt_due_at)
+
+    handle_missed_sla('frt')
+  end
+
+  def check_nrt
+    return if sla_policy.next_response_time_threshold.blank?
+    return if conversation.first_reply_created_at.blank?
+    return if conversation.waiting_since.blank?
+    return if within_threshold?(applied_sla.nrt_due_at)
+
+    handle_missed_sla('nrt')
+  end
+
+  def check_rt
+    return if sla_policy.resolution_time_threshold.blank?
+    return if conversation.resolved?
+    return if within_threshold?(applied_sla.rt_due_at)
+
+    handle_missed_sla('rt')
+  end
+
+  def within_threshold?(due_at)
+    Time.zone.now.to_i < due_at
+  end
+
+  def frt_was_hit?
+    return false if applied_sla.frt_due_at.blank?
+    return false if conversation.first_reply_created_at.blank?
+
+    conversation.first_reply_created_at.to_i <= applied_sla.frt_due_at
+  end
+
+  def handle_missed_sla(type)
+    meta = type == 'nrt' ? { message_id: last_incoming_message_id } : {}
+    return if already_missed?(type, meta)
+
+    create_sla_event(type, meta)
+    log_miss(type)
+    applied_sla.update!(sla_status: 'active_with_misses') unless applied_sla.active_with_misses?
+  end
+
+  def handle_hit_sla
+    if applied_sla.active?
+      applied_sla.update!(sla_status: 'hit')
+      log_result('hit')
+    else
+      applied_sla.update!(sla_status: 'missed')
+      log_result('missed')
     end
   end
 
-  def still_within_threshold?(threshold)
-    Time.zone.now.to_i < threshold
-  end
-
-  def check_first_response_time_threshold(applied_sla, conversation, sla_policy)
-    threshold = conversation.created_at.to_i + sla_policy.first_response_time_threshold.to_i
-    return if first_reply_was_within_threshold?(conversation, threshold)
-    return if still_within_threshold?(threshold)
-
-    handle_missed_sla(applied_sla, 'frt')
-  end
-
-  def first_reply_was_within_threshold?(conversation, threshold)
-    conversation.first_reply_created_at.present? && conversation.first_reply_created_at.to_i <= threshold
-  end
-
-  def check_next_response_time_threshold(applied_sla, conversation, sla_policy)
-    # still waiting for first reply, so covered under first response time threshold
-    return if conversation.first_reply_created_at.blank?
-    # Waiting on customer response, no need to check next response time threshold
-    return if conversation.waiting_since.blank?
-
-    threshold = conversation.waiting_since.to_i + sla_policy.next_response_time_threshold.to_i
-    return if still_within_threshold?(threshold)
-
-    handle_missed_sla(applied_sla, 'nrt')
-  end
-
-  def get_last_message_id(conversation)
-    # TODO: refactor the method to fetch last message without reply
-    conversation.messages.where(message_type: :incoming).last&.id
-  end
-
-  def already_missed?(applied_sla, type, meta = {})
+  def already_missed?(type, meta)
     SlaEvent.exists?(applied_sla: applied_sla, event_type: type, meta: meta)
   end
 
-  def check_resolution_time_threshold(applied_sla, conversation, sla_policy)
-    return if conversation.resolved?
-
-    threshold = conversation.created_at.to_i + sla_policy.resolution_time_threshold.to_i
-    return if still_within_threshold?(threshold)
-
-    handle_missed_sla(applied_sla, 'rt')
+  def last_incoming_message_id
+    Message.where(account_id: conversation.account_id, conversation_id: conversation.id, message_type: :incoming).last&.id
   end
 
-  def handle_missed_sla(applied_sla, type, meta = {})
-    meta = { message_id: get_last_message_id(applied_sla.conversation) } if type == 'nrt'
-    return if already_missed?(applied_sla, type, meta)
-
-    create_sla_event(applied_sla, type, meta)
-    Rails.logger.warn "SLA #{type} missed for conversation #{applied_sla.conversation.id} " \
-                      "in account #{applied_sla.account_id} " \
-                      "for sla_policy #{applied_sla.sla_policy.id}"
-
-    applied_sla.update!(sla_status: 'active_with_misses') if applied_sla.sla_status != 'active_with_misses'
-  end
-
-  def handle_hit_sla(applied_sla)
-    if applied_sla.active?
-      applied_sla.update!(sla_status: 'hit')
-      Rails.logger.info "SLA hit for conversation #{applied_sla.conversation.id} " \
-                        "in account #{applied_sla.account_id} " \
-                        "for sla_policy #{applied_sla.sla_policy.id}"
-    else
-      applied_sla.update!(sla_status: 'missed')
-      Rails.logger.info "SLA missed for conversation #{applied_sla.conversation.id} " \
-                        "in account #{applied_sla.account_id} " \
-                        "for sla_policy #{applied_sla.sla_policy.id}"
-    end
-  end
-
-  def create_sla_event(applied_sla, event_type, meta = {})
+  def create_sla_event(event_type, meta)
     SlaEvent.create!(
       applied_sla: applied_sla,
-      conversation: applied_sla.conversation,
+      conversation: conversation,
       event_type: event_type,
       meta: meta,
       account: applied_sla.account,
-      inbox: applied_sla.conversation.inbox,
-      sla_policy: applied_sla.sla_policy
+      inbox: conversation.inbox,
+      sla_policy: sla_policy
     )
   end
+
+  def log_miss(type)
+    Rails.logger.warn "SLA #{type} missed for conversation #{conversation.id} " \
+                      "in account #{applied_sla.account_id} for sla_policy #{sla_policy.id}"
+  end
+
+  def log_result(result)
+    Rails.logger.info "SLA #{result} for conversation #{conversation.id} " \
+                      "in account #{applied_sla.account_id} for sla_policy #{sla_policy.id}"
+  end
 end
diff --git a/enterprise/app/views/api/v1/models/_applied_sla.json.jbuilder b/enterprise/app/views/api/v1/models/_applied_sla.json.jbuilder
index e7f1c49fc..c00782622 100644
--- a/enterprise/app/views/api/v1/models/_applied_sla.json.jbuilder
+++ b/enterprise/app/views/api/v1/models/_applied_sla.json.jbuilder
@@ -9,3 +9,7 @@ json.sla_first_response_time_threshold resource.sla_policy.first_response_time_t
 json.sla_next_response_time_threshold resource.sla_policy.next_response_time_threshold
 json.sla_only_during_business_hours resource.sla_policy.only_during_business_hours
 json.sla_resolution_time_threshold resource.sla_policy.resolution_time_threshold
+sla_due_at_values = resource.due_at_values
+json.sla_frt_due_at sla_due_at_values[:frt]
+json.sla_nrt_due_at sla_due_at_values[:nrt]
+json.sla_rt_due_at sla_due_at_values[:rt]
diff --git a/spec/enterprise/models/applied_sla_spec.rb b/spec/enterprise/models/applied_sla_spec.rb
index a1433f6a2..343294b75 100644
--- a/spec/enterprise/models/applied_sla_spec.rb
+++ b/spec/enterprise/models/applied_sla_spec.rb
@@ -22,10 +22,45 @@ RSpec.describe AppliedSla, type: :model do
           sla_first_response_time_threshold: applied_sla.sla_policy.first_response_time_threshold,
           sla_next_response_time_threshold: applied_sla.sla_policy.next_response_time_threshold,
           sla_only_during_business_hours: applied_sla.sla_policy.only_during_business_hours,
-          sla_resolution_time_threshold: applied_sla.sla_policy.resolution_time_threshold
+          sla_resolution_time_threshold: applied_sla.sla_policy.resolution_time_threshold,
+          sla_frt_due_at: applied_sla.frt_due_at,
+          sla_nrt_due_at: applied_sla.nrt_due_at,
+          sla_rt_due_at: applied_sla.rt_due_at
         }
       )
     end
+
+    it 'shares the working hours cache while serializing due times' do
+      account = create(:account)
+      inbox = create(:inbox, account: account, working_hours_enabled: true, timezone: 'UTC')
+      sla_policy = create(
+        :sla_policy,
+        account: account,
+        first_response_time_threshold: 1.hour,
+        next_response_time_threshold: 30.minutes,
+        resolution_time_threshold: 2.hours,
+        only_during_business_hours: true
+      )
+      start_time = Time.zone.parse('2024-01-17 10:00:00')
+      conversation = create(
+        :conversation,
+        account: account,
+        inbox: inbox,
+        created_at: start_time,
+        waiting_since: start_time + 1.hour
+      )
+      conversation.update!(waiting_since: start_time + 1.hour)
+      applied_sla = create(:applied_sla, account: account, conversation: conversation, sla_policy: sla_policy)
+      working_hours = inbox.working_hours
+
+      expect(working_hours).to receive(:index_by).once.and_call_original
+
+      expect(applied_sla.push_event_data).to include(
+        sla_frt_due_at: Time.zone.parse('2024-01-17 11:00:00').to_i,
+        sla_nrt_due_at: Time.zone.parse('2024-01-17 11:30:00').to_i,
+        sla_rt_due_at: Time.zone.parse('2024-01-17 12:00:00').to_i
+      )
+    end
   end
 
   describe 'validates_factory' do
@@ -34,4 +69,86 @@ RSpec.describe AppliedSla, type: :model do
       expect(applied_sla.sla_status).to eq 'active'
     end
   end
+
+  describe '#frt_due_at' do
+    it 'returns nil when first_response_time_threshold is blank' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(first_response_time_threshold: nil)
+
+      expect(applied_sla.frt_due_at).to be_nil
+    end
+
+    it 'returns deadline based on conversation created_at' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(first_response_time_threshold: 3600, only_during_business_hours: false)
+
+      expected_deadline = applied_sla.conversation.created_at.to_i + 3600
+      expect(applied_sla.frt_due_at).to eq(expected_deadline)
+    end
+  end
+
+  describe '#nrt_due_at' do
+    it 'returns nil when next_response_time_threshold is blank' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(next_response_time_threshold: nil)
+
+      expect(applied_sla.nrt_due_at).to be_nil
+    end
+
+    it 'returns nil when waiting_since is blank' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(next_response_time_threshold: 1800)
+      applied_sla.conversation.update!(waiting_since: nil)
+
+      expect(applied_sla.nrt_due_at).to be_nil
+    end
+
+    it 'returns deadline based on waiting_since' do
+      applied_sla = create(:applied_sla)
+      waiting_since = 2.hours.ago
+      applied_sla.sla_policy.update!(next_response_time_threshold: 1800, only_during_business_hours: false)
+      applied_sla.conversation.update!(waiting_since: waiting_since)
+
+      expected_deadline = waiting_since.to_i + 1800
+      expect(applied_sla.nrt_due_at).to eq(expected_deadline)
+    end
+  end
+
+  describe '#rt_due_at' do
+    it 'returns nil when resolution_time_threshold is blank' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(resolution_time_threshold: nil)
+
+      expect(applied_sla.rt_due_at).to be_nil
+    end
+
+    it 'returns deadline based on conversation created_at' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(resolution_time_threshold: 7200, only_during_business_hours: false)
+
+      expected_deadline = applied_sla.conversation.created_at.to_i + 7200
+      expect(applied_sla.rt_due_at).to eq(expected_deadline)
+    end
+  end
+
+  describe '#calculate_due_at' do
+    it 'uses BusinessHoursService when only_during_business_hours is true' do
+      account = create(:account)
+      inbox = create(:inbox, account: account, working_hours_enabled: true)
+      sla_policy = create(:sla_policy, account: account, first_response_time_threshold: 3600, only_during_business_hours: true)
+      conversation = create(:conversation, account: account, inbox: inbox)
+      applied_sla = create(:applied_sla, sla_policy: sla_policy, conversation: conversation, account: account)
+
+      expect(Sla::BusinessHoursService).to receive(:new).and_call_original
+      applied_sla.frt_due_at
+    end
+
+    it 'does not use BusinessHoursService when only_during_business_hours is false' do
+      applied_sla = create(:applied_sla)
+      applied_sla.sla_policy.update!(first_response_time_threshold: 3600, only_during_business_hours: false)
+
+      expect(Sla::BusinessHoursService).not_to receive(:new)
+      applied_sla.frt_due_at
+    end
+  end
 end
diff --git a/spec/enterprise/services/sla/business_hours_service_spec.rb b/spec/enterprise/services/sla/business_hours_service_spec.rb
new file mode 100644
index 000000000..31205c934
--- /dev/null
+++ b/spec/enterprise/services/sla/business_hours_service_spec.rb
@@ -0,0 +1,184 @@
+require 'rails_helper'
+
+RSpec.describe Sla::BusinessHoursService do
+  let(:account) { create(:account) }
+  let(:inbox) { create(:inbox, account: account, working_hours_enabled: true, timezone: 'UTC') }
+
+  # Default working hours: Mon-Fri 9:00-17:00 UTC, Sat-Sun closed
+  describe '#deadline' do
+    context 'when business hours should not apply' do
+      it 'returns wall-clock deadline when working_hours_enabled is false' do
+        inbox.update!(working_hours_enabled: false)
+        start_time = Time.zone.parse('2024-01-19 16:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: start_time, threshold_seconds: 3600)
+
+        expect(service.deadline.to_i).to eq((start_time + 1.hour).to_i)
+      end
+
+      it 'returns wall-clock deadline when all days are closed' do
+        inbox.working_hours.find_each { |wh| wh.update!(closed_all_day: true) }
+        start_time = Time.zone.parse('2024-01-19 16:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: start_time, threshold_seconds: 3600)
+
+        expect(service.deadline.to_i).to eq((start_time + 1.hour).to_i)
+      end
+    end
+
+    context 'when start time is during business hours' do
+      it 'calculates deadline within the same day' do
+        # Wednesday 10:00 AM + 2 hours = Wednesday 12:00 PM
+        start_time = Time.zone.parse('2024-01-17 10:00:00') # Wednesday
+        expected_deadline = Time.zone.parse('2024-01-17 12:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: start_time, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(expected_deadline.to_i)
+      end
+
+      it 'spans to next business day when threshold exceeds remaining hours' do
+        # Friday 4:00 PM + 2 hours = Monday 10:00 AM (1h Friday + 1h Monday)
+        friday_4pm = Time.zone.parse('2024-01-19 16:00:00')
+        monday_10am = Time.zone.parse('2024-01-22 10:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: friday_4pm, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(monday_10am.to_i)
+      end
+    end
+
+    context 'when start time is before business hours' do
+      it 'starts counting from business hours open time' do
+        # Wednesday 7:00 AM + 2 hours = Wednesday 11:00 AM (starts at 9 AM)
+        start_time = Time.zone.parse('2024-01-17 07:00:00') # Wednesday 7 AM
+        expected_deadline = Time.zone.parse('2024-01-17 11:00:00') # Wednesday 11 AM
+
+        service = described_class.new(inbox: inbox, start_time: start_time, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(expected_deadline.to_i)
+      end
+    end
+
+    context 'when start time is after business hours' do
+      it 'starts counting from next business day' do
+        # Wednesday 6:00 PM + 2 hours = Thursday 11:00 AM
+        start_time = Time.zone.parse('2024-01-17 18:00:00') # Wednesday 6 PM
+        expected_deadline = Time.zone.parse('2024-01-18 11:00:00') # Thursday 11 AM
+
+        service = described_class.new(inbox: inbox, start_time: start_time, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(expected_deadline.to_i)
+      end
+    end
+
+    context 'when start time is on a closed day' do
+      it 'starts counting from next business day' do
+        # Saturday 10:00 AM + 2 hours = Monday 11:00 AM
+        saturday = Time.zone.parse('2024-01-20 10:00:00')
+        monday_11am = Time.zone.parse('2024-01-22 11:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: saturday, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(monday_11am.to_i)
+      end
+    end
+
+    context 'when threshold spans multiple days' do
+      it 'calculates correctly across multiple business days' do
+        # Monday 4:00 PM + 10 hours = Wednesday 10:00 AM
+        # Monday: 1h (4-5 PM), Tuesday: 8h (9-5), Wednesday: 1h (9-10 AM)
+        monday_4pm = Time.zone.parse('2024-01-15 16:00:00')
+        wednesday_10am = Time.zone.parse('2024-01-17 10:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: monday_4pm, threshold_seconds: 10.hours)
+
+        expect(service.deadline.to_i).to eq(wednesday_10am.to_i)
+      end
+
+      it 'reuses loaded working hours while calculating across days' do
+        monday_4pm = Time.zone.parse('2024-01-15 16:00:00')
+        wednesday_10am = Time.zone.parse('2024-01-17 10:00:00')
+        working_hours = inbox.working_hours
+        service = described_class.new(inbox: inbox, start_time: monday_4pm, threshold_seconds: 10.hours)
+
+        expect(working_hours).to receive(:index_by).once.and_call_original
+        expect(working_hours).not_to receive(:find_by)
+
+        expect(service.deadline.to_i).to eq(wednesday_10am.to_i)
+      end
+    end
+
+    context 'with different timezone' do
+      it 'respects inbox timezone' do
+        inbox.update!(timezone: 'America/New_York')
+        # Friday 4:00 PM EST + 2 hours = Monday 10:00 AM EST
+        friday_4pm_est = Time.zone.parse('2024-01-19 16:00:00 EST')
+        monday_10am_est = Time.zone.parse('2024-01-22 10:00:00 EST')
+
+        service = described_class.new(inbox: inbox, start_time: friday_4pm_est, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(monday_10am_est.to_i)
+      end
+    end
+
+    context 'when day is open all day' do
+      it 'treats the day as 24 hours of business time' do
+        # Set Saturday to open_all_day (0:00 - 23:59)
+        inbox.working_hours.find_by(day_of_week: 6).update!(open_all_day: true, closed_all_day: false)
+
+        # Saturday 10:00 AM + 2 hours = Saturday 12:00 PM
+        saturday_10am = Time.zone.parse('2024-01-20 10:00:00')
+        saturday_12pm = Time.zone.parse('2024-01-20 12:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: saturday_10am, threshold_seconds: 2.hours)
+
+        expect(service.deadline.to_i).to eq(saturday_12pm.to_i)
+      end
+
+      it 'includes the final minute in the business-time window' do
+        inbox.working_hours.find_by(day_of_week: 6).update!(open_all_day: true, closed_all_day: false)
+
+        saturday_midnight = Time.zone.parse('2024-01-20 00:00:00')
+        sunday_midnight = Time.zone.parse('2024-01-21 00:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: saturday_midnight, threshold_seconds: 24.hours)
+
+        expect(service.deadline.to_i).to eq(sunday_midnight.to_i)
+      end
+    end
+
+    context 'when days have different business hours' do
+      it 'uses the correct close time after advancing to next day' do
+        # Monday (day 1) closes at 17:00, Tuesday (day 2) closes at 20:00
+        inbox.working_hours.find_by(day_of_week: 1).update!(open_hour: 9, close_hour: 17)
+        inbox.working_hours.find_by(day_of_week: 2).update!(open_hour: 9, close_hour: 20)
+
+        # Start at Monday 18:00 (after close) + 10 hours
+        # Should start counting from Tuesday 9:00 AM
+        # Tuesday has 11 hours available (9:00-20:00), so 10 hours = Tuesday 19:00
+        monday_6pm = Time.zone.parse('2024-01-15 18:00:00') # Monday
+        tuesday_7pm = Time.zone.parse('2024-01-16 19:00:00') # Tuesday
+
+        service = described_class.new(inbox: inbox, start_time: monday_6pm, threshold_seconds: 10.hours)
+
+        expect(service.deadline.to_i).to eq(tuesday_7pm.to_i)
+      end
+
+      it 'spans correctly across days with varying hours' do
+        # Monday (day 1): 9:00-17:00 (8h), Tuesday (day 2): 9:00-20:00 (11h)
+        inbox.working_hours.find_by(day_of_week: 1).update!(open_hour: 9, close_hour: 17)
+        inbox.working_hours.find_by(day_of_week: 2).update!(open_hour: 9, close_hour: 20)
+
+        # Start at Monday 16:00 + 12 hours
+        # Monday: 1h (16:00-17:00), Tuesday: 11h remaining (9:00-20:00)
+        monday_4pm = Time.zone.parse('2024-01-15 16:00:00')
+        tuesday_8pm = Time.zone.parse('2024-01-16 20:00:00')
+
+        service = described_class.new(inbox: inbox, start_time: monday_4pm, threshold_seconds: 12.hours)
+
+        expect(service.deadline.to_i).to eq(tuesday_8pm.to_i)
+      end
+    end
+  end
+end
diff --git a/spec/enterprise/services/sla/evaluate_applied_sla_service_spec.rb b/spec/enterprise/services/sla/evaluate_applied_sla_service_spec.rb
index 71afd2125..40e361e00 100644
--- a/spec/enterprise/services/sla/evaluate_applied_sla_service_spec.rb
+++ b/spec/enterprise/services/sla/evaluate_applied_sla_service_spec.rb
@@ -140,6 +140,71 @@ RSpec.describe Sla::EvaluateAppliedSlaService do
       end
     end
 
+    context 'when first response SLA is hit after non-business hours' do
+      let(:created_at) { Time.zone.parse('2026-06-25 00:39:56 UTC') }
+      let(:wall_clock_breach_time) { Time.zone.parse('2026-06-25 01:40:03 UTC') }
+      let(:first_reply_created_at) { Time.zone.parse('2026-06-25 11:45:36 UTC') }
+      let(:post_reply_eval_time) { Time.zone.parse('2026-06-25 11:46:38 UTC') }
+      let(:email_inbox) { create(:inbox, :with_email, account: account, working_hours_enabled: true, timezone: 'America/New_York') }
+      let(:business_hours_sla_policy) do
+        create(
+          :sla_policy,
+          account: account,
+          first_response_time_threshold: 1.hour,
+          next_response_time_threshold: nil,
+          resolution_time_threshold: nil,
+          only_during_business_hours: true
+        )
+      end
+      let(:business_hours_conversation) do
+        create(
+          :conversation,
+          account: account,
+          inbox: email_inbox,
+          sla_policy: business_hours_sla_policy,
+          created_at: created_at,
+          last_activity_at: created_at
+        )
+      end
+      let(:business_hours_applied_sla) { business_hours_conversation.applied_sla }
+
+      before do
+        {
+          0 => [11, 0, 20, 0],
+          1 => [7, 0, 20, 0],
+          2 => [7, 0, 20, 0],
+          3 => [7, 0, 20, 0],
+          4 => [7, 0, 16, 0],
+          5 => [7, 0, 16, 0],
+          6 => [11, 0, 20, 0]
+        }.each do |day_of_week, (open_hour, open_minutes, close_hour, close_minutes)|
+          email_inbox.working_hours.find_by(day_of_week: day_of_week).update!(
+            open_hour: open_hour,
+            open_minutes: open_minutes,
+            close_hour: close_hour,
+            close_minutes: close_minutes,
+            closed_all_day: false,
+            open_all_day: false
+          )
+        end
+      end
+
+      it 'does not mark FRT missed while outside business hours or after an on-time business-hours reply' do
+        travel_to wall_clock_breach_time do
+          described_class.new(applied_sla: business_hours_applied_sla).perform
+        end
+
+        business_hours_conversation.update!(first_reply_created_at: first_reply_created_at, last_activity_at: first_reply_created_at)
+
+        travel_to post_reply_eval_time do
+          described_class.new(applied_sla: business_hours_applied_sla).perform
+        end
+
+        expect(business_hours_applied_sla.reload.sla_status).to eq('active')
+        expect(SlaEvent.where(applied_sla: business_hours_applied_sla, event_type: 'frt')).not_to exist
+      end
+    end
+
     context 'when next response SLA is hit' do
       before do
         applied_sla.sla_policy.update(next_response_time_threshold: 6.hours)
@@ -191,16 +256,16 @@ RSpec.describe Sla::EvaluateAppliedSlaService do
       # Simulate conversation timeline
       # Hit frt
       # incoming message from customer
-      create(:message, conversation: conversation, created_at: 6.hours.ago, message_type: :incoming)
+      create(:message, conversation: conversation, account: conversation.account, created_at: 6.hours.ago, message_type: :incoming)
       # outgoing message from agent within frt
-      create(:message, conversation: conversation, created_at: 5.hours.ago, message_type: :outgoing)
+      create(:message, conversation: conversation, account: conversation.account, created_at: 5.hours.ago, message_type: :outgoing)
 
       # Miss nrt first time
-      create(:message, conversation: conversation, created_at: 4.hours.ago, message_type: :incoming)
+      create(:message, conversation: conversation, account: conversation.account, created_at: 4.hours.ago, message_type: :incoming)
       described_class.new(applied_sla: applied_sla).perform
 
       # Miss nrt second time
-      create(:message, conversation: conversation, created_at: 3.hours.ago, message_type: :incoming)
+      create(:message, conversation: conversation, account: conversation.account, created_at: 3.hours.ago, message_type: :incoming)
       described_class.new(applied_sla: applied_sla).perform
 
       # Conversation is resolved missing rt