Technically, you can start to get your Masters once you're inducted. Of course, realistically, you won't have much time until your first shore tour. So, let's just look at the law of averages here and say you take 2 years from start to finish of flight school. Then another year or less in the RAG, then 36+ months at your fleet sea tour (these are Navy numbers, Marine numbers will vary). If you take less time in flight school, then obviously you'll end your fleet sea tour sooner, but you get the idea.
As for the Navy paying for the degree, they usually want some kind of payback if you use Tuition Assitance. Generally they want a year for every year of TA you use. I don't know what the current rules are, but for a while, you could count your current time in as the time you owe, so theoretically could wrap up your degree and time owed for the degree by the time your commtment was over. However, if you go OCS, you can sign up for the GI Bill, which won't incurr any more obligation (but does cost something like a $1000 to sign up). This is an incredibly good deal, and can be used during or after your military service. You can even transfer it to your kids now.
