the program has 4-5 workouts per week, and ramps up intensity over time. Earlier workouts have less reps and intensity (e.g. you’ll do 50 burpees per session). They only increase intensity if you can handle more. https://www.youtube.com/watch?v=RHUTgKWNUCs
OP, not sure how much you expect to see from 3 sessions. HIIT will almost certainly improve your stamina and recovery, if you emphasize the Intensity part of the name, and can you help tone up. I’ve steadily lost weight over months doing it, with absolutely zero change to my diet, which is neither the healthiest nor the crappiest. And I am/was not that big. But your starting point, were you a crappy eater, how lean/big are you, will probably influence your results. If the end game is muscle mass, then HIIT probably shouldn’t be your main focus.
The answer is nothing. OP is long gone (or is he?). You a-holes damn near gave me a heart attack bumping a thread by xray.