I'm sure you will make a decision that is best for you and your husband, avian, but I do have to comment that given all the people I've seen on here who are desperate for respite care, or who have asked, but not been able to get it, that if you are being offered respite, just say yes! One of the things I've learnt about dementia is that when anyone offers help, I should just accept it, even if I think I don't need help.
I would also take as long a respite period as is possible.
As to how to convince your husband to go, I've seen several strategies mentioned here. One is to have the doctor inform your husband that he (your husband) must go to respite (always let someone else deliver the message/be the bad guy/take the fall when possible--it keeps the onus off you), either for his benefit, yours, or both. Another is for you to tell your husband the doctor has ordered it. Another is to just state that you must have a break and so he is going--no discussion. Perhaps others here have additional suggestions?
I hope this works out for you.