At age 13 the 13 year old should get at least 9 to 11 hours of sleep at night especially if it's on school nights.
So if the 13 year old needs to get up at 6:00 AM to get ready for school then the 13 year old should go to bed at 8:00 PM to 9:00 PM
On Weekends the 13 year old might stay up until 11:00 PM before going to bed since the 13 year old could sleep in on the weekends.
So make sure the 13 year old goes to bed at a proper time of the night to allow at least 9 hours of sleep through the night.
Also factor in the time it takes to actually fall asleep which can sometimes be as long as 30 minutes.
When I was 13 years old I went to sleep around 8:00 PM and was asleep by 8:30 PM on school nights.
On days when I didn't have school I would stay up until 11:00 PM and sometimes as long as 12:00 PM and then sleep in on the weekends.