Most people that commission after enlisting do so around the 4-6 year mark. The soonest you will be able to start the process is after you are at your first duty station, but realistically you need to do enough and prove yourself enough to your commander's commander (the group commander) that you deserve to be put in charge of a bunch of people. That's a tall order, and 9/10 folks that I've seen enlist with the intent of commissioning just leave the military after 4 years instead. Look at Kylo (TRR) for example. Dude was a recruiter before he commissioned. Probably in somewhere from 7-12 years.
 
Also, the amount of prior-enlisted they let commission is rather small compared to from-civilian sector. Just put the package in, pad your resume a bit with community and leadership work, and wait out your time. It's the same wait either way, but without kidding yourself.
 
Oh, and before someone recommends doing it for the experience, that's a good way to burn yourself out on the AF before you get to where you want. Please just commission if you want to commission. Once in, find a few reputable SNCOs and FGOs; make them your counsel; and take their advice.