Now as for Black Belt. There are standards, and if you aren't up to the standards in both hours and ability, I wouldn't bet on a black belt within the USAF. USAF also requires you to attend two seminars a year. Basically, go out and see the Shihans! lol
If your ability or days are not up to snub, you won't pass. (Typically when your hours aren't up, your ability isn't up either, generally! There are exceptions.)
I know people from at least 2 people from 2 dojos that passed dan exams in the USAF without having the hours, though only they and their senseis probably know the whole truth (the number of hours written on the form is not necessarily always accurate). Then again even they may not be sure, not everybody keeps especially complete or accurate records of attendance.
For me, my criteria when preparing for an exam is simple. Can I do what is expected and not embarrass myself or my sensei? The rest I leave to others (my senseis, the technical committee, etc.) to figure out.