These settings apply to the time shown in the status bar at the top of the screen, and in world clocks and calendars.
Choose General > Date & Time and turn 24-Hour Time on or off. (Not available in all countries.)
Choose General > Date & Time and turn Set Automatically on or off.
If iPhone is set to update the time automatically, it gets the correct time over the cellular network, and updates it for the time zone you’re in.
Some carriers don’t support network time in all locations. If you’re traveling, iPhone may not be able to automatically set the local time.
Choose General > Date & Time and turn Set Automatically off. Tap Time Zone and enter the name of a major city in your time zone. Tap the “Date & Time” return button, then tap “Set Date & Time” and enter the date and time.