Last year, when I was in res...
10 minutes...grab food//get to class if they're far apart
1 hour...either work on an assignment/prelab or find a nice cozy spot to read a magazine (I love the fake "window seats" between the lockers in BSB)
2+ hours...head back to res for some quality facebooking/movie watching/nap time. Or last minute cramming, depending on the time of year.
But this year, it won't be quite so convenient to grab a nap between classes, so I'll be using breaks of an hour or more to review notes/prep for classes/work. I sure will miss nap time though...they became an integral part of my day
.