My sims have had time to socialize every night and join clubs, etc. even with a 3 course class load each term. As long as you attend classes and take notes, you don't have to do much of anything else outside of the classroom. I always enroll in the term on friday late afternoon and get all the term papers/presentations done by Saturday afternoon....leaving plenty of free time for the rest of the term.
Edit: I should mention, I've only ever gone to university with Sims who entered with at least 3-4 skill levels in their core skills and some Research & Debate skill right as they entered Uni, developed when they were still children/teens. i.e. I haven't taken any sims through university which weren't born in game. The Research & Debate skill in particular helps a lot.
I also always have a few levels of handiness for all my played sims and I upgrade their beds, even when they stay in the dorm. Less sleep needed = more time for other stuff.
