It varies.
For example hornet is in CA, getting his Ph.D straight out of the AFA(2010), he will be at pilot training this fall. Eagle got his Masters straight out of the AFA too. There is a poster on the ROTC forum, their DS is going straight to Wright Pat for AFIT (grad school)
LITS got his this past weekend, after he got out, but started while he was in the CG.
Bullet got his as an O3, using TA. It extends your commitment time. In the AF you will probably not find an O5 without a grad degree.
Your moniker to me says you are not thinking about the AF, but Navy, Marines or Army.
The question is why you want an MBA?
The fact is your leadership skills from a management POV, and intricate knowledge in the defense world, will make you more competitive to certain companies/organizations than your peers that did 2 yrs more getting the grad degree from a top knot college with no knowledge. Think SAIC, Booze Allen, L3 Comm, Raytheon, Rand, TI, Lockheed, Grumman, Pratt and Whitney, GE defense, etc. That is before you even look at GS jobs.
xposted with LITS.
Notice the common response...why/what you want with an MBA?