I'd be cautious listening to anything that coach says if he is advising such sporadic and bizarre t3 dosing. Exo t3 WILL shut down your friends own thyroid output while using it ... and t3's half life isn't particularly long .... there is a reason all the literature for people on t3 therapy are told to take it daily (some advise split daily spread out) I personally use it daily in the AM with my GH prior to fasted cardio. Using it sporadically like the coach is advising just sounds like trouble for your friends body, and yo-yo'ing of his metabolism which is the last thing you want when prepping. If his metabolism is decent as is I'd honestly advise against it in general. Better to utilize diet, cardio, Clen, tren, etc.
This is coming from someone who self administers t3/t4 therapy year round on themselves, and I have been doing so for damn near 8 years. finding one's 'sweet spot' dosage wise can be a bitch and result in accelerated muscle loss, or, the opposite side - accelerated fat gains.