Hopefully your hubby will get back into his normal sleep pattern soon but then it will get disrupted again with his 2nd TKR. I'm sure, in the end, he will feel it was all worth it. I'm so in awe of how well his recovery has gone and can only wish the same for myself.
I'm a person that just has to have my sleep or I'm not worth a plug nickel. I need 7 uninterrupted hours a night at least, 8 is better and 9 is optimal for me. Although I don't remember the last time my body let me sleep much more than 7.