Things You'll Need
Instructions
Remove your "Pokemon Sapphire" game from the Nintendo DS.
Press the power button to turn on the system.
Tap the screen when the "Touch the Touch Screen to continue" message appears.
Tap the "Settings Menu Panel" at the bottom-middle part of the screen, when the main menu appears.
Select the calendar/time icon. It's the blue icon, second from the left.
Tap the calendar or the clock icon, depending on whether you want to change the date or the time. Tap the up/down arrows above each number to change the date and time to whatever is most convenient for the Pokemon you're trying to capture. When you're done, just tap the "Confirm" button in the lower-right corner.
Wait for the confirmation message to go away, then tap "Go Back," "Quit" and "Yes" to exit back to the main menu. The DS will shut down and save your new settings.
Put your "Pokemon Sapphire" cartridge back in the DS, and it will start with your new date and time loaded.