I'm home schooled so I don't really have set times. I usually start at 9 and when I finish just depends on how much work I do that day. But it's usually between 1 and 3. sometimes more...
EDIT: I get a lot of people saying that's not long compared to normal school. But keep in mind I don't take long lunch breaks, don't have to walk from class to class, wait for the teacher to arive to the class, dont have to listen to the teacher talk about things I've already learned, or get distracted. (I got really distracted at school. First kids talking and mucking around, then teacher screaming at them, and repeat, repeat, repeat)