I'm fairly new to this, going into my 3rd year, so this advice could be worth less than you gave for it. (But it's working for me).
I wait for a day when it is warm and sunny enough to have lots of bees flying. You don't say what type of treatment you plan to use, vapor or dribble. I use vapor and make sure there's another hour or two of warm sunshine before treating so they can settle back down and re-cluster before it gets cold again.
I've never done the dribble method, so won't provide any input on that.
Edited to add:
I would be very reluctant to dribble liquid in the hive anytime during winter.
A forum community dedicated to beekeeping, bee owners and enthusiasts. Come join the discussion about breeding, honey production, health, behavior, hives, housing, adopting, care, classifieds, and more!