Sometimes AA will open up more T (coach award) inventory as the departure date gets closer. You could wait as late as the original departure time to decide. If T inventory opens up before then, change your coach award to the desired date. If it doesn't open up, "save" the ticket by changing it to a date way in the future, then try again some other weekend.

AA might (or might not) open up more T inventory. It's a gamble. But let's face it: you're headed to VEGAS, so it should be no problem to do some additional gambling as part of the travel arrangements.