You can always apply for FAP (whenever applications are open), but my understanding is that they will not refund any fees paid before FAP is approved. So, you not only need to apply, you also need to be approved, and I have no idea how long that takes. You'll either have to hold off on registering for the MCAT until you are approved, or accept that you will have to pay for that registration.
From the AAMC website:
Fee Assistance Program benefits are NOT retroactive. Benefits may only be applied after the Fee Assistance Program benefits have been awarded. For example, if you pay full fees for an MCAT registration and your Fee Assistance Program application is later approved, the MCAT registration fees will not be refunded. Also, you will not be able to use your awarded medical school designations if your AMCAS application was submitted before your Fee Assistance Program application was approved. The AAMC is not responsible for any MCAT registration deadlines or medical school application deadlines you may miss while waiting for the review of your Fee Assistance Program application. No refunds will be issued if you pay full fees for an MSAR subscription, MCAT registration or an AMCAS application, for example, those fees will not be refunded if your Fee Assistance Program application is later approved. All sales are final on AAMC products.
