Mine took all winter Supposedly if you up their protein, they go through it quicker, although mine got extra high protein snacks all winter and didin't help.
My girls just started a couple of weeks ago.......blowing feathers out left and right! Egg production is what I am most concerned with, I can live with ugly chickens.
So far the egg production is just down a little bit.....like from 5-6 eggs a day to 3 or so. I feed these girls pretty darn good, protein wise, so hopefully the egg production doesn't drop off to bad. I can't eat feathers.
It really varies. Some breeds rarely molt. Like RIR or production breeds. The ones that seem to loose all their feathers at once will usually be done within 6 weeks. The ones that molt slower can take a lot longer but some of them might still lay an egg here or there. In my experience the longest might take 3-4 months.