Molting question

Depends on the age and health of the bird. Figure about 2 months.

 

These sites might interest you. I think they kind of answer your question. It's good information anyway.

Mississippi State describes molting
http://msucares.com/poultry/management/poultry_feathers.html

Kansas State feather loss
http://www.ksre.ksu.edu/library/lvstk2/mf2308.pdf

I could read your question a couple of different ways. If you mean, how long does a molt last, it varies. The K State link answers that. If your question is when will they molt, the main cause of molting is the days getting shorter, but other things can cause it. Running out of water for a while, being scared by a predator, anything that stresses them can cause it.