Instructions
Wake the Tamagotchi when you wake in the morning instead of allowing it to wake at the factory scheduled time. Giving it a few extra hours in the morning will force it to age faster. Press the B button on the character screen to get to the clock. Press A and C simultaneously to stop the clock, and change the time with the A button. Use the B button to confirm your change, then press C to resume.
Change the clock back to the normal time halfway through the day to give your Tamagotchi a chance to normalize. Play with your Tamagotchi as usual.
Set the clock back three or so hours in the evening to give your Tamagotchi a total of 5-6 extra hours of growth per day.
Repeat these steps until your Tamagotchi reaches the age you desire.
Pause the clock on the Tamagotchi for one to two hours once it reaches your desired age to slow the rapid growth back to normal.