You son must submit his CFA form as part of his admission package if he wants the Admission Board to review his package for Scholastic Qualification (one of the three "Qs" is the Triple Qualification).
Candidates should submit all forms of the application as soon as possible to be competitive. The deadline for submitting all forms is March 1st. Once a candidate has submitted the CFA and all the other forms, their package will trip and be pushed in front of the Board. The Board meets weekly from August through mid-April.
Sooooo, if your son has all the other forms in his package submitted, he may only need to take it once theoretically.
I would not wait till March 1st. Nominations are closing out the end of October and as soon as noms start to hit the system the Board is going to start going active on appointment offers.