Well I just finished grad school last year and it took me 3 1/2 years-- our spring break was usually the 1st or 2nd week in March. I believe it was the same as an undergrad. However, we went the 1st week in March last year and there were very little crowds! We never waited on line more than 10-20 minutes, and didn't have any problems catching busses (we stayed at the ASMovies). I recommend this time of year-- besides the low crowds, the weather was perfect! But I heard it can be chillly.... But for me, I would rather a little chilly than 95 degrees!
Hope this helps!