About the same in class as outside of class.
In my case - Triple maths (AM) - Means 3 hours after school on hw. Although I generally do a bit more to really understand everything. I have a very strong work ethic, which my friends hate me for - you know - "oh, we've all got homework, come out for a bit". No. I want an A thanks. I can see so many people that are going to get a U/E in my year.
so yeah, Time in school = time outside school. About 20-25 hours/week.