We paid the full $17,500 from our 529 to our mid's account during his youngster year. The school uses it to first pay off whatever part of his initial uniform loan is still unpaid. Once that happens, the loan repayment is no longer taken out of their monthly pay, so they do make a little more than other mids until those are paid off--usually beginning of 2/c year. After that, while it doesn't increase his regular monthly pay, he still gets it. A few times (maybe 3?) times a year, the USNA disbursing office disburses money to the mids called "held pay." This is a certain amount of money that the office holds out of their paycheck for additional expenses that the mids may accrue--like books, football tickets, who knows what else. Whatever is not used is distributed during one of those held pay payments up to $750 per payment. Most mids get maybe $200 or so, though firsties generally end up with more and plebes generally get very little. Held pay feels like Christmas. Since we gave our son's account the money, he gets the max $750 for each of those scheduled dispersals. He can also go into the dispersing office and request an individual dispersal once a month. So if he remembers to go in and fill out the paperwork, he gets the $750 each month in addition to his pay. I'm not sure how early you can start requesting disbursements--maybe not as a plebe? Any money still left over in the account will get paid out at graduation.
I'm not sure if I think this is the greatest way to do it (especially now with the roth option) since you're entrusting a bunch of your hard-earned money to a kid who may not appreciate its value, but it turned out we had more in our 529 than we were going to need and didn't want to pay a tax penalty on it. We made an agreement with him that he would save the majority of the money toward a down payment on a house (or equivalent) and not go on wild spending sprees as a mid.
