Don't know how long but remember they are protein based and whatever organism "eats" them when they are unattached from chick may also "eat" feathers on attached chick. Protein is mostly amino acid compounds and when they breakdown they give off "amines". God made amines smell really bad so we'd stay away from rotting meat (and bodies). Now a hand ful may not be so bad but if you are talking large amount as in just plucked after hatcet duty, I wouldn't. Make sure chickens do not have access to compost and let the SMELLS begin!
Thanks for replies. I have pine shavings in my coop, and the feathers are all mixed in with everything. I don't know how I would separate them! I'm not sure if there are so many feathers because my chickens are almost 4 months old, and getting new "grown up" feathers, but there are tons of feathers everywhere!