I like to sleep at least 6 hours per day, and 7 is better -- so let's say 7.
Family matters, eating, bathing, taking care of normal life -- 8 hours/day.
Guitar Practice -- 4 to 5 hours per day -- say 4.
Delcamp moderating -- 1 to 2 hours per day.
Video games including XBox 360 -- 4 hours per day.
Windsurfing -- 4 to 6 hours per day, say 5 as a good average.
Movies, TV, relaxing -- about 7 hours per week or 1 hours per day.
That adds up to: 30 to 31 hours per day. So, going to school should be no problem, just add another 6 hours per day plus 4 hours for study and you should be about 40 hours per day, but you can usually count on only a half day of 20 hours on Saturday, and many places you can get Sunday off... unless you are studying Classical Guitar -- in which case you need to practice more on the weekends.
Go for it.
"Things should be made as simple as possible, but not any simpler" A. Einstein