diff --git a/e2e-tests/assistant-search.spec.ts b/e2e-tests/assistant-search.spec.ts
index 2be490c3..3a5782e5 100644
--- a/e2e-tests/assistant-search.spec.ts
+++ b/e2e-tests/assistant-search.spec.ts
@@ -1,10 +1,12 @@
+import { FALLBACK_LANGUAGE } from '@atb/translations/commons';
 import { test, expect } from '@playwright/test';
 
 const JST = 'Asia/Tokyo';
 const EET = 'Europe/Helsinki';
-const CTU = 'Europe/Oslo';
+const CET = 'Europe/Oslo';
 const UTC = 'Europe/London';
 const PST = 'America/Los_Angeles';
+const IST = 'Asia/Kolkata';
 
 const fromTextbox = 'Kristiansund';
 const fromOption = 'Kristiansund trafikkterminal';
@@ -13,6 +15,29 @@ const toOption = 'Molde trafikkterminal';
 const searchTime = '15:30';
 const expectedDeparture = '16:00 -';
 
+const localTimeCET = new Date().toLocaleTimeString(FALLBACK_LANGUAGE, {
+  timeZone: CET,
+  hour12: false,
+  hour: '2-digit',
+  minute: '2-digit',
+});
+
+function timeDifferenceInMinutes(time1: string, time2: string): number {
+  const [hour1, minute1] = time1.split(':').map(Number);
+  const [hour2, minute2] = time2.split(':').map(Number);
+
+  const totalMinutes1 = hour1 * 60 + minute1;
+  const totalMinutes2 = hour2 * 60 + minute2;
+
+  return Math.abs(totalMinutes1 - totalMinutes2);
+}
+
+// True if the difference between time1 and time2 is less than 60 minutes.
+function sameTimezone(time1: string, time2: string): boolean {
+  const minutesDifference = timeDifferenceInMinutes(time1, time2);
+  return minutesDifference < 60;
+}
+
 test.describe('Trip search from different timezones - detailed view.', () => {
   test.beforeEach(async ({ page }) => {
     await page.goto(process.env.E2E_URL ?? 'http://localhost:3000');
@@ -69,9 +94,9 @@ test.describe('Trip search from different timezones - detailed view.', () => {
   });
 
   test.use({
-    timezoneId: CTU,
+    timezoneId: CET,
   });
-  test(CTU + ' - (UTC +0100)', async ({ page }) => {
+  test(CET + ' - (UTC +0100)', async ({ page }) => {
     await page.getByTestId('searchTimeSelector-departBy').click();
     await page.getByTestId('searchTimeSelector-time').click();
     await page.getByTestId('searchTimeSelector-time').fill(searchTime);
@@ -142,4 +167,107 @@ test.describe('Trip search from different timezones - detailed view.', () => {
 
     expect(elementText?.includes(expectedDeparture));
   });
+
+  test.use({
+    timezoneId: IST,
+  });
+  test(IST + ' - (UTC +0550)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    await page.getByTestId('searchTimeSelector-time').fill(searchTime);
+    await page.getByRole('textbox', { name: 'From' }).click();
+    await page.getByRole('textbox', { name: 'From' }).fill(fromTextbox);
+    await page.getByRole('option', { name: fromOption }).click();
+    await page.getByRole('textbox', { name: 'To' }).click();
+    await page.getByRole('textbox', { name: 'To' }).fill(toTextbox);
+    await page
+      .getByRole('option', {
+        name: toOption,
+      })
+      .click();
+    await page.getByTestId('tripPattern-0-0').click();
+    const elementText = await page
+      .getByTestId('detailsHeader-duration')
+      .textContent();
+
+    expect(elementText?.includes(expectedDeparture));
+  });
+});
+
+test.describe('Adjusts for summer and winter time - detailed view.', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto(process.env.E2E_URL ?? 'http://localhost:3000');
+  });
+
+  test.use({
+    timezoneId: JST,
+  });
+  test(JST + ' - (UTC +0900)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
+
+  test.use({
+    timezoneId: EET,
+  });
+  test(EET + ' - (UTC +0200)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
+
+  test.use({
+    timezoneId: CET,
+  });
+  test(CET + ' - (UTC +0100)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
+
+  test.use({
+    timezoneId: UTC,
+  });
+  test(UTC + ' - (UTC +0000)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
+
+  test.use({
+    timezoneId: PST,
+  });
+  test(PST + ' - (UTC -0800)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
+
+  test.use({
+    timezoneId: IST,
+  });
+  test(IST + ' - (UTC +0550)', async ({ page }) => {
+    await page.getByTestId('searchTimeSelector-departBy').click();
+    await page.getByTestId('searchTimeSelector-time').click();
+    const departureTime = await page
+      .getByTestId('searchTimeSelector-time')
+      .inputValue();
+    expect(sameTimezone(localTimeCET, departureTime)).toBeTruthy();
+  });
 });
diff --git a/src/modules/search-time/selector/index.tsx b/src/modules/search-time/selector/index.tsx
index a2ed936e..a0e1ce12 100644
--- a/src/modules/search-time/selector/index.tsx
+++ b/src/modules/search-time/selector/index.tsx
@@ -8,7 +8,7 @@ import {
 } from '@atb/translations';
 import { SEARCH_MODES, SearchMode, SearchTime } from '../types';
 import style from './selector.module.css';
-import { formatLocalTimeToCET, setTimezone } from '@atb/utils/date';
+import { fromLocalTimeToCET, setTimezone } from '@atb/utils/date';
 
 type SearchTimeSelectorProps = {
   onChange: (state: SearchTime) => void;
@@ -25,7 +25,7 @@ export default function SearchTimeSelector({
   const [selectedMode, setSelectedMode] = useState<SearchTime>(initialState);
   const initialDate = setTimezone(
     'dateTime' in initialState
-      ? new Date(formatLocalTimeToCET(initialState.dateTime))
+      ? new Date(fromLocalTimeToCET(initialState.dateTime))
       : new Date(),
   ) as Date;
 
diff --git a/src/page-modules/assistant/client/journey-planner/index.ts b/src/page-modules/assistant/client/journey-planner/index.ts
index 21da9d2f..151b404d 100644
--- a/src/page-modules/assistant/client/journey-planner/index.ts
+++ b/src/page-modules/assistant/client/journey-planner/index.ts
@@ -9,7 +9,7 @@ import { swrFetcher } from '@atb/modules/api-browser';
 import useSWRInfinite from 'swr/infinite';
 import { createTripQuery, tripQueryToQueryString } from '../../utils';
 import { useEffect, useState } from 'react';
-import { formatLocalTimeToCET } from '@atb/utils/date';
+import { fromLocalTimeToCET } from '@atb/utils/date';
 import { LineData } from '../../server/journey-planner/validators';
 
 const MAX_NUMBER_OF_INITIAL_SEARCH_ATTEMPTS = 3;
@@ -47,7 +47,7 @@ export function useTripPatterns(
           ...tripQuery,
           searchTime: {
             ...tripQuery.searchTime,
-            dateTime: formatLocalTimeToCET(tripQuery.searchTime.dateTime),
+            dateTime: fromLocalTimeToCET(tripQuery.searchTime.dateTime),
           },
         },
   );
diff --git a/src/page-modules/assistant/details/utils.ts b/src/page-modules/assistant/details/utils.ts
index beb4c524..b313b046 100644
--- a/src/page-modules/assistant/details/utils.ts
+++ b/src/page-modules/assistant/details/utils.ts
@@ -1,4 +1,4 @@
-import { formatCETToLocalTime } from '@atb/utils/date';
+import { fromCETToLocalTime } from '@atb/utils/date';
 import { parseTripQueryString } from '../server/journey-planner';
 
 export function formatQuayName(quayName?: string, publicCode?: string | null) {
@@ -53,7 +53,7 @@ export function tripQueryStringToQueryParams(
   const fromLayer = from.place?.includes('StopPlace') ? 'venue' : 'address';
   const toLayer = to.place?.includes('StopPlace') ? 'venue' : 'address';
   const searchTime = String(
-    formatCETToLocalTime(new Date(originalSearchTime).getTime()),
+    fromCETToLocalTime(new Date(originalSearchTime).getTime()),
   );
 
   const params = {
diff --git a/src/utils/date.ts b/src/utils/date.ts
index 11680b5e..3465b467 100644
--- a/src/utils/date.ts
+++ b/src/utils/date.ts
@@ -370,18 +370,70 @@ export function setTimezone(date: Date): Date {
   return new Date(date.toLocaleString(FALLBACK_LANGUAGE, { timeZone: CET }));
 }
 
-export function formatLocalTimeToCET(localTime: number) {
-  const offset = getOffsetTimezone();
-  return localTime + ONE_HOUR * (offset - 2);
+export function fromLocalTimeToCET(localTime: number) {
+  const hoursDifference = getHoursDifferenceFromCET(localTime); // difference from CET.
+  return localTime + ONE_HOUR * hoursDifference;
 }
 
-export function formatCETToLocalTime(cet: number) {
-  const offset = getOffsetTimezone();
-  return cet - ONE_HOUR * (offset - 2);
+export function fromCETToLocalTime(cet: number) {
+  const hoursDifference = getHoursDifferenceFromCET(cet);
+  return cet - ONE_HOUR * hoursDifference;
 }
 
-function getOffsetTimezone() {
-  return (-1 * new Date().getTimezoneOffset()) / 60;
+function getUTCOffset(date: Date, timeZone: string): number {
+  const offsetString = date
+    .toLocaleString('ia', {
+      timeZoneName: 'longOffset',
+      timeZone,
+    })
+    .replace(/^.*? GMT/, '');
+
+  const [offsetHour, offsetMinutes] = offsetString.split(':');
+  const utcOffset =
+    parseInt(offsetHour || '0') +
+    (offsetMinutes ? parseInt(offsetMinutes) / 60 : 0);
+
+  return utcOffset;
+}
+
+export function getHoursDifferenceFromCET(time: number, timeZone?: string) {
+  const date = timeZone
+    ? new Date(new Date(time).toLocaleString('en-US', { timeZone }))
+    : new Date(time);
+
+  let offsetUTC;
+  if (timeZone) offsetUTC = getUTCOffset(new Date(time), timeZone) * -60;
+  else offsetUTC = date.getTimezoneOffset();
+  const isDST = isDaylightSavingTime(date);
+
+  let offsetCET = 1; // Winter time
+  if (isDST) offsetCET = 2; // Summer time
+
+  let hoursDifferenceToCET = -(offsetCET + offsetUTC / 60);
+
+  // If 0 heours difference, remove '-'
+  hoursDifferenceToCET = hoursDifferenceToCET === -0 ? 0 : hoursDifferenceToCET;
+
+  return hoursDifferenceToCET;
+}
+
+export function isDaylightSavingTime(date: Date): boolean {
+  const dstStart = getLastSundayOfMonthAndSetTime(date.getFullYear(), 2, 2); // Last Sunday of March at 02:00
+  const dstEnd = getLastSundayOfMonthAndSetTime(date.getFullYear(), 9, 3); // Last Sunday of October at 03:00
+
+  return date >= dstStart && date < dstEnd;
+}
+
+export function getLastSundayOfMonthAndSetTime(
+  year: number,
+  month: number,
+  hour: number,
+) {
+  let daysInMonth = new Date(year, month + 1, 0).getDate();
+  const date = new Date(year, month, daysInMonth);
+  date.setDate(date.getDate() - ((date.getDay() + 7) % 7)); // Last sunday in month
+  date.setHours(hour); // Set time.
+  return date;
 }
 
 export function dateWithReplacedTime(
diff --git a/src/utils/date/__tests__/date.test.tsx b/src/utils/date/__tests__/date.test.tsx
new file mode 100644
index 00000000..01f03dce
--- /dev/null
+++ b/src/utils/date/__tests__/date.test.tsx
@@ -0,0 +1,87 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  getHoursDifferenceFromCET,
+  getLastSundayOfMonthAndSetTime,
+  isDaylightSavingTime,
+} from '@atb/utils/date';
+
+describe('isDaylightSavingTime', () => {
+  const winterTime = new Date(2024, 0, 2);
+  const summerTime = new Date(2024, 6, 2);
+
+  it(`should rejects that date ${winterTime} is within daylight saving time (DST).`, () => {
+    const isWhitinDST = isDaylightSavingTime(winterTime);
+    expect(isWhitinDST).toBeFalsy();
+  });
+
+  it(`should confime that date ${summerTime} is within daylight saving time (DST).`, () => {
+    const isWhitinDST = isDaylightSavingTime(summerTime);
+    expect(isWhitinDST).toBeTruthy();
+  });
+});
+
+describe('getCETOffset', () => {
+  const timezones = [
+    { name: 'Asia/Tokyo', etcOffsetWinterTime: 8, etcOffsetSummerTime: 7 },
+    { name: 'Europe/Helsinki', etcOffsetWinterTime: 1, etcOffsetSummerTime: 1 },
+    { name: 'Europe/Oslo', etcOffsetWinterTime: 0, etcOffsetSummerTime: 0 },
+    { name: 'Europe/London', etcOffsetWinterTime: -1, etcOffsetSummerTime: -1 },
+    {
+      name: 'America/Los_Angeles',
+      etcOffsetWinterTime: -9,
+      etcOffsetSummerTime: -9,
+    },
+    {
+      name: 'Asia/Kolkata',
+      etcOffsetWinterTime: 4.5,
+      etcOffsetSummerTime: 3.5,
+    },
+  ];
+
+  timezones.forEach((timezone) => {
+    it(`should return the offset from Europe/Oslo to ${timezone.name}.`, () => {
+      const winterTime = new Date(2024, 0, 2);
+      let hoursDifference = getHoursDifferenceFromCET(
+        winterTime.getTime(),
+        timezone.name,
+      );
+      expect(hoursDifference).toEqual(timezone.etcOffsetWinterTime);
+    });
+
+    it(`should return the offset from Europe/Oslo to ${timezone.name} when DST in Norway.`, () => {
+      const summerTime = new Date(2024, 6, 2);
+      let hoursDifference = getHoursDifferenceFromCET(
+        summerTime.getTime(),
+        timezone.name,
+      );
+      expect(hoursDifference).toEqual(timezone.etcOffsetSummerTime);
+    });
+  });
+});
+
+describe('getLastSundayOfMonthWithTime', () => {
+  it('should return the date of the last sunday in given year, month, and with specified time.', () => {
+    const year = 2024;
+    const march = 2;
+    const day = 31;
+    const hour = 2;
+
+    const dateLastSundayInMarch2024 = new Date(year, march, day, hour);
+    const result = getLastSundayOfMonthAndSetTime(year, march, hour);
+
+    expect(result).toEqual(dateLastSundayInMarch2024);
+  });
+
+  it('should return the date of the last sunday in given year, month, and with specified time.', () => {
+    const year = 2024;
+    const october = 9;
+    const day = 27;
+    const hour = 3;
+
+    const dateLastSundayInOctober2024 = new Date(year, october, day, hour);
+    const result = getLastSundayOfMonthAndSetTime(year, october, hour);
+
+    expect(result).toEqual(dateLastSundayInOctober2024);
+  });
+});