I wouldn't count on them "noticing" your leave request and automatically delaying your class up date. Your best bet is to wait until a time when the STU CON officer isn't swamped with A-pool student issues, go in in Khakis, and very succinctly explain your situation. 1. This trip has been planned for some time. 2. Your parents gave it to you as a graduation present (or whatever the reason was) 3. It was a surprise, and you really didn't have any say in when it was scheduled. 4. You are more than willing to have your class up date pushed back, if that makes it easier for them to accomodate your request.
Obviously, you will have to tailor this to your individual situation, but if 7 years in the Navy has taught me anything, there are a few basics that will help whenever you ask for anything special. 1. Don't do it when they have 50 other things demanding their attention. 2. Don't make it their problem; make it clear that you understand this is a special request, and that you've already tried to look at the possible conflicts, (such as their finely tuned production schedule) and find a way to make your request impact them as little as possible (let them shift your class up date later, if it helps their scheduling). 3. Don't wait until the last minute. This will just p!ss them off and make them much less willing to go out of their way to help you. 4. Finally, be aware that by requesting a special, out of the ordinary favor from them, they may do the same in return. If you get that call a few days after your trip telling you to take a stash job shoveling sh!t at the dog pound, realize it's your obligation to help them out, the same way they helped you. Sorry for the long winded answer, maybe you can tell I've been on both sides of this situation before, and good luck with your trip!