How often do you take the flight physical once you're active duty?
Once a year, usually in your birth month or the month right before that.
There are a couple circumstances when you might do more than one in a year-
If it's going to be due while you're deployed and you won't be able to get it done on deployment, then they'll work around that (might mean you see the flight doc right before you deploy and then again right after you get back).
When you first join, everybody going to flight school gets one when they first get to Pensacola. After that, you always do it in your regular month, even if the flight school flight physical was a few months before your birthday (unless the flight school one was the month prior to your birth month, then it also counts as your regular annual flight physical).
The EKG and the moon river surprise aren't every year, they work a little different.