I can speak from personal experience as I actually kept strict logs my senior year of how much work I was doing. Mind you at the time I was taking some grad classes, but it really wasn't unusual work loads compared to the people around me. I spent between 15-25 hours in class per week. I worked (teaching assistant) about 10 hours a week. I spent about 50-60 hours per week on homework, labs and general studying. And I did a varsity sport, which took about 3-4 hours per day. On most days, I would wake up at 5am, go to practice, go straight to class, stay on campus and study until 10 or 11 at night and then go to bed. Weekends would be similar. If I was lucky, I would get 1 night off a week.

I don't know where some of the other commenters get the idea that students these days don't take the time to study. I can't comment a lot about Harvard, but at my school, it was difficult to come across a student who wasn't taking a full load of courses (more often than not double or triple majors), involved in several extracurricals and often doing work study.