iCloud: Change your calendar’s time zone
The default time zone for your calendars (and their events) is the time zone you set when you set up your iCloud account. However, by turning on time zone support, you can create events and view calendars in time zones other than your default time zone. If you’re in the Pacific time zone (Pacific daylight time), but you wish to create or view events for the eastern time zone (eastern standard time), time zone support lets you do so.
If time zone support is on, your calendar doesn’t update if you move between time zones. For example, if you have a meeting at 10 a.m. Pacific time in California, and you fly to New York, that meeting still appears at 10 a.m. in iCloud Calendar.
If time zone support is off, your calendar moves as you move; that is, the time zone settings update as you change time zones. For example, if you have a meeting at 10 a.m. Pacific time in California and fly to New York, your calendar items are shown in local (eastern) time. So your meeting at 10 a.m. Pacific time shows up at 1 p.m. eastern time.
Use a time zone other than the default time zone
In iCloud Calendar, choose Preferences from the Action pop-up menu at the top of the window.
Click Advanced, select the “Enable time zone support” checkbox, then click Save.
With time zone support on, a “time zone” pop-up menu appears when you create an event, letting you set any time zone you want.
You can also reset the default time zone for your calendars (and their events) at any time.