Yet another answer that is summarized by: It Depends. (But probably not a good idea for this one)
Whenever I design a workout for a client, there are a few things I ask myself regarding an exercise, and they go something along these lines…
1) Does it get my client closer to their goal?
2) Is this sound physiology and proper program design?
3) Can this client perform this exercise properly AND at its intended intensity?
So number one, I don’t know because I don’t have any information for this client.
Number two, depends, but probably not. As important as the exercise being performed is the ability of the body to recover. How your body responds and recovers is the true limiting factor in making gains, not how much weight is on the bar or how fast you do something. After a true HIIT workout, your body is going to need to recover.
Conditioning like sleds and sprints, I could buy that, but I would rather do it 2-3 days a week on non-consecutive days. Chances are if they actually need this training, their program should be well thought out. That doesn’t include 3 in a row with that type of training.
Not to mention true “HIIT” workouts are controversial themselves.
Number three, I don’t know and probably not. Day 3 is going to be tough, meaning probably a little slack. Lack of execution and good technique mixed with fatigue leads to injuries quickly.
In short, I wouldn’t do three days. Space it out, assign it for homework if you need to. There are hundreds of other things you could do.