If you go Aviation, your commitment is after you get your wings. So if you go jets, it's 8 years after your wings...for helos/props, it's 7.
I don't know the exact wait time now (others have mentioned it on the boards), but basically, after you're commissioned, you'll wait anywhere from 0-2 months, then start. For helos, it's about a year and a half. For props, John can answer it better, but it's about the same, from what I gather. For Jets it's longer, I'd guess at least 2 years till you get to the RAG. I didn't do OCS, but I believe that's 13 weeks.