Re: Winter Broodless Period for Northern Latitudes.
I am also in USDA zone 7a, although considerably more south. My queens typically stop laying toward the end of October and are back into production in January. Broodless might be a six week period between mid Nov and New Year's. Timing treatments of OAV for around Thanksgiving and Christmas works well for almost the entire country. Some bees never go entirely broodless, unless the queen died, so waiting for that mystical, magical moment may be in vain.
Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.