Yesterday I installed the second box. It may have been a couple of days too soon but, I knew that I would not be able to get to them for many days. Anyway, I put the second box on the hives on Thursday and today there is a lot of activity at the entrance so I am hopefully confident that they are doing alright with the split up brood/nest.
I plan on leaving them alone for at least a week until I check on them again. (I think they will and deserve some alone time). I am hoping that I have done the right thing.