Jim,
I graduate the 18th of May as well, however the Navy doesn't start paying you as an E-5 until they get your final grades, which makes it like 2 weeks less but it's still nice. As for moving up your date, I know there is a post on here refering to a date moving up I think it is "OCS date curveball" or something like that. My date has never moved, it was on my accecptance letter into OCS. However I'd tend to think that a move-up is fightable.
JT