The iPhone automatically updates which time zone you’re in, assuming you’re using the default setting (you can change this in Settings > General > Date & Time > Set Automatically). However, the behavior of the iPhone’s calendar depends on another feature called Time Zone Support. This feature is located in Settings > Mail, Contacts, Calendars > Time Zone Support. Unfortunately, this setting is quite confusing and not terribly functional.
Time Zone Support ON
When Time Zone Support is on (the default setting), the calendar will always display events according to the time zone selected below the Time Zone Support toggle switch. An example: Let’s assume this time zone is set to New York. If you travel to California, your phone’s clock will change to California time, but your calendar will still display events in New York time and when you add new events they will default to the New York time zone. To view events in California time, you will have to change this setting manually. However, with Time Zone Support on, you have the option of changing the time zone for each calendar event that you create or edit (the Time Zone field appears below the “Ends:” field when editing an event).
Time Zone Support OFF
When Time Zone Support is off, the calendar displays events according to the phone’s current time zone. An example: If you live in New York and you travel to California, your calendar will automatically switch to display all of your events in California time. So if you added an event while in New York that starts at 10am, that event will display in California starting at 7am. If you add an event while in California that starts at 10am, it will display as starting at 1pm when you get back to New York. With Time Zone Support off, there’s no way to change the time zone of an event when creating or editing.
Which is better?
Each has its own advantages and disadvantages. With Time Zone Support off, you never have to worry about changing settings to view calendar events according to your local time zone. However, you must be careful when entering new events–if you’re in California scheduling a meeting that will take place in New York the following week, you must make the time adjustment yourself (a 10am meeting will need to be entered as starting at 7am). With Time Zone Support on, you must dive into the Settings app to change your calendar’s time zone each time you travel, but you have the convenience of entering new events in a specific time zone–in the above example, you can just set that meeting for 10am and set the time zone to New York without making the calculation in your head.