I usually requeen in the late summer/early fall...for the following reasons...
(1) The main honey flow is over and you are not disrupting the bees in the midst of the main flow.
(2) Queens are in high demand in early Spring and thus many of the breeders run out of stock...however in the late Summer and early Fall, Queens are more readily available.
(3) Sometimes you get a better price for Fall Queens than in the early Spring.
When requeening in the Fall, I try to give myslef enough time to order a replacement queen should I have acceptance problems. Ok...hope this helps. Of course, there may be others who will promote Spring requeening over Fall...but what I've shared is what I have done. God bless and good luck!
