As JMs mentioned; you're senior year is going to be busy. Hopefully, the academy isn't the only place you are applying to for college. You are going to have other college applications; redoing ACT/SAT; then all the normal school stuff; and the excitement of being a senior.
I'm totally in favor of getting your entire academy application and your MOC nomination applications done immediately. And if you are physically fit and will have no problem with the CFA, then I suggest you get it all done early. When I have contact with applicants in the spring of their juniro years (April-May), and they are interested in applying to the academy, I have them line up everything prior to school getting out for the year. Teacher's email addresses, admin mailing school profile, transcripts, etc... I try and get them to get their entire application; including MOC nomination, Medical and CFA, all completed before school starts again at the end of August. This frees them to enjoy school and apply to their other schools.
Plus, if you're one of the first MOC applications going to your senator/representative, it can't hurt to show you have some initiative and motivation.