Final answer:
AR 600-9 standards apply to IET Trainees upon completion of Basic Combat Training (BCT), which is when they start to follow the body composition and physical readiness standards.
Step-by-step explanation:
The standards of AR 600-9 are applicable to IET (Initial Entry Training) Trainees upon completion of BCT (Basic Combat Training).
The regulations which include body composition and physical readiness standards become effective for these trainees as soon as they have graduated from Basic Training and have moved on to their next phase of training, which could be Advanced Individual Training (AIT), Officer Candidate School, or other related training programs.