The academy will give you a deadline for the entire application depending on how early you submitted and passed the pre-candidate questionnaire. You can only take the CFA officially once any time before your application deadline for the air force academy. For USNA, I have heard that they let you take it multiple times. However, once you submit your CFA scores for USAFA, if they are passing scores, you cannot take it again. If they are not deemed passing by the admissions board, then they may or may not offer a retake.