What date should I have my northern overwintered nucs made up by ? I may have started them to soon this year. Will have to start pulling brood frames soon.
I made my nucs mid August last year and bought mated queens. That was pushing it for Michigan I think. A brood cycle takes 21 days and you hope to get some foragers and numbers going before frost. My nucs all made it thru winter, but I gave them electric heat and used polystyrene insulated nucs. I think it would be wiser to start earlier and simply pull frames of brood if they're getting too strong.
How early would also depend upon rather you are going to let the bees make their own queen and mate with local drones (hope they're around), or if you're going to buy a mated queen.
This is a case where it's probably better to error on the early side, rather than the late side :)
The folks best known here in VT for doing it (kirk webster and Michael Palmer) both suggest mid july and possibly early august on a good year. Both of them are breaking down less productive colonies for raw material and adding mated queens to the new nucs.