how much do you practice?

Ok im just curious about something because i've never really read or heard about it. How much do professional riders actually PRACTICE? I'm not talking about just going out and riding, i mean actually goin out and figuring out what and where and how they are doing something wrong. How many times do they ride a week? How many hours per day? is there really a limit on how much you can ride in one day before you are actually not improving anymore? do they do drills? just a few questions i had.