You go to the first icon where it has your Tamagotchis stats, and you press the A button until it shows a list of three options. You press the B button, and then press it again to select the first option which enables you to set the time. The second option on the list is to turn the sound on and off, and the third option is to adjust the contrast.
If its not too late... Adjust the time to sleeping time for your tama. If its young enough, there is a tama daycare for 50 points. Either will cover care of your tama for the duration.
one last thing. if im not mistaken, an adult can alrady go to school which is aomthing like day care but has no cost. this is from RaTamaZone's videos. thanks ra!