Hey, man!
I once was apart of the college life, and I ran into the same dilemma. I still work 40+ hours a week, too, but I still managed to rise to my Plat I promos on my off days. Introductions out of the way, here's my advice:
First off, I hope you have a smart phone. There's an app for the League of Legends wikia. Get it. Just browse it for a few mintues whenever you're waiting on a professor to start class. Waiting in the break room at work. On the toilet! Seriously, I learn something new just about every time I get on there. After you have the app, start playing out imaginary laning scenarios in your head. I play three roles with less than a dozen champions. I rarely come across a match up that I don't know how to play with my main. Runes. Masteries. Skill priority. How to behave in lane, and what to do after. These are all decisions you should be making in champion select, and you don't need to play a game to practice that!
Next thing is study game theory. It seems a little odd, but there are archetypal decisions that you will make every game. Making the right decisions is how you improve and win games. There's a reason the meta exists, and that's because the decisions you make in champion select, as well as the game, are how you win.
Lastly, be efficient. Do not waste time. Be decisive.