I don't know if there is a general rule for the best sleep, it surely varies from person to person.

The normal thing would be to wake up in the morning when the sun rises, it is instinctive for animals and logical/instinctive for us. Our ancestors had to take advantage of most of the day before the dangers of the night.

In my case I need 6:30-7 hours of sleep, not too much nor less, if I have more or less than that it is difficult for me to get up.