you need at least 8 hours of sleep
About 9pm! So hurry up!
As soon as you can. Maybe 8, or at the latest 10, but if you're not in bed at least by 11 or 12 you'll be sorry in the morning
Between 9 and 10 pm it's ok.
you go to school on a sunday?
before 10 pm , early to bed is early to rise