Because from 12 to 3 pm, it is a deep sleep period. As long as you have a good sleep in these three hours, you can be energetic all day. It usually takes 30-60 minutes from falling asleep to entering deep sleep, so it is best to sleep at 10: 00- 10: 30 at night.
As for the time to get up, scientific research shows that getting up between 6: 00 and 6: 30 in the morning, preferably around 6: 30, is most beneficial to your health.