You can it whenver you want and actually I like the idea of having it sooner. For my friends her's was 3 months before and with chipping in for everything, it was easier on my pocket this way. Then I didn't have to worry about the wedding present cost on top of the party cost. It does make it finacially easier for everyone coming speacially if they're throwing in for fees for the party. And I think it was easier on her as the bride to have it earlier to. Then it was said and done and soemthing she got to check of her list. Do what you want. And Vegas sounds like fun and you should enjoy it whenever you want to go!!