I would not plan on going out that often while you're in school. I hate to say this but the barn sucks up important study time.
You should definitely allow yourself 30 minutes 1 day.. and maybe build up but not THAT much... I am balancing a fulltime job, horse time, and college online. I have been dedicating Saturdays to my 30 minutes of riding (now it's 50 at this new barn) and have just ended my term so I am able to spend a few hours out there once a week with my new project. But yeah between travel time, groom time, and ride time.. the minimum I can be out there is 3 hours..
"Strength is the ability to use a muscle without tension"