Anywhere from 6 to 12 months after first talking to the recruiter, to shipping to basic training.
2. You do NOT get to choose the AFSC you want in the AF.
You will list 5 AFSC's at MEPS, then they will decide if you get one of those 5 AFSC's, an open aptitude area contract or they offer a completely different AFSC.
All job assignments are competitive
IE: job assignments are based on who has the highest qualifying MAGE score, those with the highest score who want the job, get assigned the job first.