How to Add World Clocks to an iPhone
When you tap the Home button to wake your iPhone, you see the time on the screen. You set that time on the World Clock function of your iPhone's Clock app. You can also set up clocks from other time zones to keep you informed of what time it is in your overseas office or in the country where your sister is studying.
You only see four or five clocks at a time (depending on your iPhone model), but you can scroll down the list and have as many clocks as there are time zones.
Follow these steps:
Tap Clock on the Home screen.
Tap the World Clock button in the bottom left corner.
Tap the plus sign in the upper right corner.
A search field and a list of cities appears.
Scroll through the list of cities or begin typing the city or country that you want to add a clock for.
If you type S, both Scotland and San Rafael come up, as does Detroit, U.S.A. The more letters you type, the narrower your search results.
Tap the city you want to add.
If you don't see the exact city you were searching for, tap one that's in the same time zone.
The World Clock screen returns.
You see the city you chose added to the list. Tap on the time to reveal analog-style clocks instead of a digital readout. The clock has a white face if it's daytime in that city and a black face if it's night.
Tap the Edit button in the upper left corner to do one or both of the following:
Rearrange the list order: Tap and hold the reorder button on the right, and then drag the clock to the position you want.
Delete a clock: Tap the red button on the left and then tap the Delete button that appears to the right.
Tap Done after you finish.
Turn 24-hour time on or off in Settings→General→Date & Time.