On the USAF side, at least, O-1s and O-2s should never make choices about ANYTHING in their career based on perceptions/beliefs/rumors/conventional wisdom about chances of future promotion.
By the time one gets to the O-4 and above ranks where promotions are truly competitive, it's 10 years down the road in your career. 10 years might as well be a lifetime in the military, and just about anything and everything can change during that time. Whatever is 'true' today will very likely be different by the time you get to that point...including your own personal desires about what you want from the military and life.
The number O-1s I saw who were in Phase III UPT or at FTUs who were so deeply concerned about where and when they were doing their master's degrees, or were doing them concurrently, was very disconcerting.
Their job should be sitting in the vault and getting smart. However, Big Blue has certainly conditioned them early.