First make sure non of your Icons are lit up next press the B button and your time should come up. Next B and A button and your time will be blinking. Enter in the right time then hit B until your time starts running again.
Thats ok, because you change your date on that very same Timepage also. Just follow what I put in the last post and you'll be fine. The date will be the first thing blinking and just press the A button to select the day and month you want. If you make a mistake you can always go back with the C button.