As a background, I'm gonna give a little of my routine. I wake at 6:00, have class until 11:45, have lunch -not always at home- and have classes again from 2:00 to 5:10 and go to bed -depending on my sleep- at 9:00 or 10:00. Thrice a week I still have other classes after that, so that I have only about 9 hours of free time to play and study at the weekdays.
After getting home, studying and doing my papers for college, I'm usually so tired that I have no will to play, and even if I do practice, it won't be very efficient.
What can I do to, at the very least, not lose technique and keep my hands fast and flexible (and how long should I do it)?
Are there any exercises that can be done away from the piano?
Thank you and sorry if I wasn't very clear, my English has been getting worse by the day since I stopped studying it.