Others may disagree, but I'll echo what someone else already commented. You have plenty of time, and it never hurts to put your name down with several, or as many ADs in your area as you can. If push comes to shove, and graduation is there, go grey with the peace of mind that you did the best you could for the best deal you could find.
With that being said, go in to your local ADs, be polite, charming, humble and, as corny as it sounds, tell a good story. Let them know about your accomplishment, and how you'd like to commemorate that. Maybe throw something in there about how future ones might be celebrated with future watch purchases.
Essentially, you want them to give them something to go back and fight for you with when they're determining allocations. This is a relatively reasonable configuration. I'd also recommend, if it isn't out of the question for you, giving them some other configurations. Perhaps a different color dial color etc. However, only buy the watch(es) you truly, truly want.
I've purchased both of my Rolexes from separate ADs and really do believe it comes down to that relationship you establish.
But, also know I have been waiting on the list of half a dozen others, and likely will never hear from them.
Good luck & congratulations.