1) It's 5-6 hours per day when you include the weekend
2) They barely do any academic work at all - if there is an athlete in actually rigorous classes, he's the exception to the rule, and he'll have study halls and personal tutors booked for him so he can maintain his grades.
3) Adding on to point 2, most athletes who aren't there to "play school" either do one of two things: either they're forced by their coaches and/or the "athlete academic compliance department" (the people who aren't affiliated with the team, but make sure the athletes keep up their GPAs and try to get them learn a tiny bit) to go to class and there's someone checking every day to make sure they're their, or they are placed into paper classes.
Paper classes are ones where attendance isn't mandatory and that only rely on a final paper as a grade; see the quote below for an example of an athlete's paper that received an A-.
"On the evening of December Rosa Parks decided that she was going to sit in the white people section on the bus in Montgomery, Alabama. During this time blacks had to give up there seats to whites when more whites got on the bus. Rosa Parks refused to give up her seat. Her and the bus driver began to talk and the conversation went like this. “Let me have those front seats” said the driver. She didn’t get up and told the driver that she was tired of giving her seat to white people. “I’m going to have you arrested,” said the driver. “You may do that,” Rosa Parks responded. Two white policemen came in and Rosa Parks asked them “why do you all push us around?” The police officer replied and said “I don’t know, but the law is the law and you’re under arrest."