It's always easiest to treat chickens at night after they've gone to roost, at least if your coop is such that you can get in there with them. I've used different thick greasy substances such as vaseline (petroleum jelly), cocoa butter, and coconut oil, all to good effect, and there is no need of egg withdrawal with these products. The thick grease smothers the mites, gives relief from itch, helps heal the dry scales and promotes growth of new healthy scales. I treat one night then again five nights later, and a final time five nights after that. I don't even have to take my chickens off the roost, I just go down the line quickly and smear every leg; they don't fuss much about it.