The iPhone 4 features a built in clock that either sets manually or automatically to your cell phone service provider's network clock. If the current time displayed on your iPhone is slow, you can current the displayed time by manually changing the time displayed on the clock. Once you manually correct the displayed time, your iPhone will continue to display the correct time.
Tap the "Settings" button on your iPhone.
Select the "General Option."
Tap the "Date & Time" button.
Move the switch located to the right of "Set Automatically" to the "OFF" position.
Tap the "Set Date & Time" button.
Manually adjust the time dials to the correct time.
Press the Home button on your iPhone to save your new settings and correct the clock's displayed time.