I go to WOU (remember guys there are more than 3 universities in oregon---) and while I have yet to actually sew in my dorm, I've had plenty of time to do so.
I'm in a freshman dorm, LANDERS but it's the largest freshman dorm and there's plenty of space (...for a one-room shared dorm, anyways.) and next year I'll be moving into a larger, 3-room dorm. Tons of space. I brought my machine with me in the middle of the term to work on a halloween costume (only to discover that my idea was against the rules so i had to scrap it ;-; ) and brought some fabrics and things... When you're not using it it's easy to store the machine to the side, put the fabrics in drawers... I'm not really seeing how this is that difficult. I took the minimum number of credits, but the average is just 3 more, so those 3 hours spread out over an entire week can't possibly be that bad. Just make time. If it's important to you, finish your homework early or whatever and then get to it. I've found time to beat 2 full length console rpgs, work on many pictures, do all my homework, eat adequately, see my friends, and sleep. You're supposed to learn this time management crap in college anyways.
But even if working during the school days is hard, you have breaks. Long, wonderful breaks... I sew very very quickly, so maybe this is less of an issue for me than for others, but if you can get to it and just devote some time it should be easy to keep cosplaying. During high school I sewed mostly during breaks and on weekends anyways.
My school's smaller, and has a dry campus (not that that really means anything in terms of the drinking going on, but if people are being loud you can bust them) but as long as you don't have a screaming sewing machine it shouldn't really bother people if you keep the door closed and maybe do quieter things in the "quiet hours" of the dorm.