I have a flock of about 35 chickens. When I hatch out eggs or sell them I want to make sure that they are pure and not cross bred. I have Delawares, Lemon Orps, Lavender Orps and EE'S. I let them all free range together, but when I want to get pure bred eggs I have an area to separate them all by breed. My question is how long would I need to keep them separated to insure that I am not selling or hatching out a cross breed chicken? Can the hen stay fertilized from a mating that took place days ago? Mine are not laying or anything yet, but should start within the next few weeks. They are about 15 weeks old. I am most interested in the Lemon Orps and don't want to keep the Lemon Orps together for a couple of days and the eggs I collect still be fertilized by another rooster. Any advice?