Not really sure how it works in the Air Force or Navy. In the Army, we access students into HPSP after school start date a lot more than we would like to. This is a recruiting issue that is a topic for another conversation. The Army is able to separate stipend from the tuition and books. Meaning that if you commission after the school start date, the Army pays for the tuition that you would have received at the board date. The stipend cannot be started until you are officially in HPSP (boarded, scrolled, oathed, signed a contract. If you board in say, September, but started school started in August, the Army will pay for the entire first semester, but will not pay stipend until the date of the oath.