There is some magical number of days which if you have less of, you have to get TAC approval for, in order to go under. I think its around 2 weeks or so, but typically, if you want more than that, its possible as well as filling your summer up to the brim.
I had about 10 days off last week. Most of my classmates had closer to 3 weeks. Its all dependent on what you choose to do for your summer details.