From a3c5156b2fe8168121f4ff90b6e5d1206750f82c Mon Sep 17 00:00:00 2001
From: Douglas Fabris <devfabris@gmail.com>
Date: Fri, 24 Apr 2026 19:11:52 -0300
Subject: [PATCH 1/2] feat: add canonicalizeTimezone function and update
 timezone handling in settings

---
 apps/meteor/client/hooks/useTimezoneNameList.ts           | 3 ++-
 .../Setting/inputs/SelectTimezoneSettingInput.tsx         | 3 ++-
 .../views/omnichannel/businessHours/EditBusinessHours.tsx | 3 ++-
 packages/tools/src/timezone.ts                            | 8 ++++++++
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/apps/meteor/client/hooks/useTimezoneNameList.ts b/apps/meteor/client/hooks/useTimezoneNameList.ts
index e51d8812ac2c9..2cb37b7843523 100644
--- a/apps/meteor/client/hooks/useTimezoneNameList.ts
+++ b/apps/meteor/client/hooks/useTimezoneNameList.ts
@@ -2,7 +2,8 @@ import { useMemo } from 'react';
 
 const getTimeZoneNames = (): string[] => {
 	const intl = Intl as typeof Intl & { supportedValuesOf?(key: 'timeZone'): string[] };
-	return typeof intl.supportedValuesOf === 'function' ? intl.supportedValuesOf('timeZone') : [];
+	const names = typeof intl.supportedValuesOf === 'function' ? intl.supportedValuesOf('timeZone') : [];
+	return names.includes('UTC') ? names : ['UTC', ...names];
 };
 
 export const useTimezoneNameList = (): string[] => useMemo(() => getTimeZoneNames(), []);
diff --git a/apps/meteor/client/views/admin/settings/Setting/inputs/SelectTimezoneSettingInput.tsx b/apps/meteor/client/views/admin/settings/Setting/inputs/SelectTimezoneSettingInput.tsx
index 9db35413302f6..8008be82d8f06 100644
--- a/apps/meteor/client/views/admin/settings/Setting/inputs/SelectTimezoneSettingInput.tsx
+++ b/apps/meteor/client/views/admin/settings/Setting/inputs/SelectTimezoneSettingInput.tsx
@@ -1,4 +1,5 @@
 import { Field, FieldHint, FieldLabel, FieldRow, Select } from '@rocket.chat/fuselage';
+import { canonicalizeTimezone } from '@rocket.chat/tools';
 import type { ReactElement } from 'react';
 
 import { useTimezoneNameList } from '../../../../../hooks/useTimezoneNameList';
@@ -38,7 +39,7 @@ function SelectTimezoneSettingInput({
 			<FieldRow>
 				<Select
 					id={_id}
-					value={value}
+					value={typeof value === 'string' ? canonicalizeTimezone(value) : value}
 					placeholder={placeholder}
 					disabled={disabled}
 					readOnly={readonly}
diff --git a/apps/meteor/client/views/omnichannel/businessHours/EditBusinessHours.tsx b/apps/meteor/client/views/omnichannel/businessHours/EditBusinessHours.tsx
index 9c6ad2a986348..05288e002224b 100644
--- a/apps/meteor/client/views/omnichannel/businessHours/EditBusinessHours.tsx
+++ b/apps/meteor/client/views/omnichannel/businessHours/EditBusinessHours.tsx
@@ -1,6 +1,7 @@
 import type { ILivechatBusinessHour, LivechatBusinessHourTypes, Serialized } from '@rocket.chat/core-typings';
 import { Box, Button, ButtonGroup } from '@rocket.chat/fuselage';
 import { useEffectEvent } from '@rocket.chat/fuselage-hooks';
+import { canonicalizeTimezone } from '@rocket.chat/tools';
 import { Page, PageFooter, PageHeader, PageScrollableContentWithShadow } from '@rocket.chat/ui-client';
 import { useToastMessageDispatch, useTranslation, useRouter, useEndpoint } from '@rocket.chat/ui-contexts';
 import { useId } from 'react';
@@ -14,7 +15,7 @@ import { useRemoveBusinessHour } from './useRemoveBusinessHour';
 
 const getInitialData = (businessHourData: Serialized<ILivechatBusinessHour> | undefined) => ({
 	name: businessHourData?.name || '',
-	timezoneName: businessHourData?.timezone?.name || 'America/Sao_Paulo',
+	timezoneName: canonicalizeTimezone(businessHourData?.timezone?.name || 'America/Sao_Paulo'),
 	daysOpen: (businessHourData?.workHours || defaultWorkHours()).filter(({ open }) => !!open).map(({ day }) => day),
 	daysTime: (businessHourData?.workHours || defaultWorkHours())
 		.filter(({ open }) => !!open)
diff --git a/packages/tools/src/timezone.ts b/packages/tools/src/timezone.ts
index d418457d955aa..7fcb172b7cba1 100644
--- a/packages/tools/src/timezone.ts
+++ b/packages/tools/src/timezone.ts
@@ -34,3 +34,11 @@ export const guessTimezoneFromOffset = (offset: string | number): string => {
 };
 
 export const guessTimezone = (): string => new Intl.DateTimeFormat().resolvedOptions().timeZone;
+
+export const canonicalizeTimezone = (name: string): string => {
+	try {
+		return new Intl.DateTimeFormat(undefined, { timeZone: name }).resolvedOptions().timeZone;
+	} catch {
+		return name;
+	}
+};

From 9b69d163f2255724cde3eacfe86cbc1a9afb230e Mon Sep 17 00:00:00 2001
From: Douglas Fabris <devfabris@gmail.com>
Date: Fri, 24 Apr 2026 19:12:00 -0300
Subject: [PATCH 2/2] test: add unit tests for canonicalizeTimezone function

---
 packages/tools/src/timezone.spec.ts | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 packages/tools/src/timezone.spec.ts

diff --git a/packages/tools/src/timezone.spec.ts b/packages/tools/src/timezone.spec.ts
new file mode 100644
index 0000000000000..27db79edd8058
--- /dev/null
+++ b/packages/tools/src/timezone.spec.ts
@@ -0,0 +1,29 @@
+import { canonicalizeTimezone } from './timezone';
+
+describe('canonicalizeTimezone', () => {
+	it('returns the same value for a canonical IANA zone', () => {
+		expect(canonicalizeTimezone('America/Sao_Paulo')).toBe('America/Sao_Paulo');
+	});
+
+	it('resolves plain UTC to UTC', () => {
+		expect(canonicalizeTimezone('UTC')).toBe('UTC');
+	});
+
+	it('resolves Etc/UTC and Etc/GMT to UTC', () => {
+		expect(canonicalizeTimezone('Etc/UTC')).toBe('UTC');
+		expect(canonicalizeTimezone('Etc/GMT')).toBe('UTC');
+	});
+
+	it('resolves legacy moment aliases to their canonical zone', () => {
+		expect(canonicalizeTimezone('GMT')).toBe('UTC');
+		expect(canonicalizeTimezone('Zulu')).toBe('UTC');
+		expect(canonicalizeTimezone('Universal')).toBe('UTC');
+		expect(canonicalizeTimezone('US/Pacific')).toBe('America/Los_Angeles');
+		expect(canonicalizeTimezone('Japan')).toBe('Asia/Tokyo');
+	});
+
+	it('returns the input unchanged when it is not a recognized zone', () => {
+		const input = 'Not/A_Zone';
+		expect(canonicalizeTimezone(input)).toBe(input);
+	});
+});