Same amount as any student who has a coop, work meeting, club trip, or anything else.
Athletes do not miss class more than other students. I only had one athlete from any sport who ever had to miss class for games.
The athletes don't have it any tougher than other students, and have plenty of extra advantages.
I don't totally agree with this...it matters what level and what sport the athlete is in. My son runs cross country and track at a Division 2 school...he has to work his class schedule so that he doesn't have an 8 AM class (most distance running is at a morning 530 AM practice) and minimizes Friday classes. And, many of the things that a Division 1 school gets (training table, tutors, upgraded dorms, etc.) don't exist at most Division 2 schools. In this case, no scholarships (or very limited), morning practices from 530 to 730 AM, afternoon practice from 330-530 PM (lifting, flex, intervals), meets, academic expectations, own your own for food, studies, and other responsibilities.
Now does a major Division 1 athlete have extra advantages...sure. But the time commitment for the sport on top of normal student commitments is huge.