philmont,
You are not contracted until you pass the PFT and submit the required paperwork (SS card, Birth Certificate, etc).
The college you attend may have you report before the traditional cadet for their ROTC program, but that varies unit by unit. It is not a AROTC requirement, it is school by school.
For example VT may require you show up 1 week prior to the non-ROTC freshman for orientation. Whereas, NCSU requires only 2 days prior. Not implying that is fact, just an example.
Both will mandate that you pass the PFT administered to contract. Until that point you are just a scholarship recipient not contracted.
OBTW, FYI, when you show up make sure you bring the SS card (not laminated) and your original BC to contract.
Copies or laminated will delay contracting even if you pass the PFT.
Additionally, understand that as a contracted books are paid for, but it is reimbursement, which usually occurs in Oct. You will shell out the money, and sometime in Oct/Nov they will pay it back. There is no credit in your child's account for books at the college in Aug.
They will also break the book stipend in 1/2. AFROTC is 900, that means 450 per semester. If the books cost 225, you get 225. There is no 225 credit to the next semester. If they cost 500, they pay you 450, they will not say you have 400 for next semester (Total 900; 1st 500, 2nd 400)
The devil is really in the details.