How long should I use BLU-KOTE?

[Michigan Chickman]

I have 29 RIR hens and two roos. The hens are getting to be barebacks and I think it's as much from them picking as it is the roos. I started putting blu-kote on them a couple weeks ago and I can see feathers blooming on some of them. I put the treatment on them every couple days. Also, can the blu-kote get into my eggs in some way?

Thanks for your help!