Wow, Cyn, I'm not really sure....are there any rehab nurses out there?
I think you should be around to check on him while he is in it, and shift him slightly every hour or two to prevent pressure point problems. I would have him out of it at night, because you can't be around to monitor him. Maybe you could increase the amount of time he is in it each day and just take it day by day.
Hopefully he will start trying to stand up and put some weight on his feet. If that happens, it won't be such a worry, he will be relieving the pressure himself. Since we don't know exactly what the injury is, it is going to be a fly-by-the-seat-of-your-pants therapeutic intervention, LOL.
By now, you can probably read him pretty well. You may be able to tell if he is getting too tired or needs a break from it. Maybe others will have some additional ideas!