Ditto, when my female cochins start getting a little pink in their combs, I'll separate my bantams. They may not lay for over a month after that, but I'll be ready when they are. If I get a surprise egg before that, it'll be time to separate everyone--and I'll probably hatch it anyway, just to see what I've got. I have no problem with mutts, but I'd like to sell pure chicks next spring from my silky and frizzle lines. Probably early February, I'll also either separate out my mutt chickens from my barred rocks (standards in the other coop), or just remove my BO roo so I can have pure BR chicks--at least then I'll be able to sell just pullets if I have someone who wants them sexed.