How to breed chickens from a mixed flock

Hello,

For varied reasons I have a mixed flock of White Leghorns, Rhode Island Reds and ISA Browns. I will shortly be adding Barred Plymouth Rock and Black Java's. As I work through figuring out which breed I want to keep in my homestead I want to be able to breed and hatch my own chicks. I plan on keeping 1 or 2 roosters of each breed and then put a rooster and some hens in a separate breeding coop. My question is how long do I need to wait before I know the eggs coming out of those hens were fertilized from that rooster and not from another rooster when they were all together in one flock?

Thanks,
Jerry

Roosters tend to be very protective, so the 1 that you see in a group of 1 to 10 that is a rooster will most likely fertilize the eggs of that group. Just keep their boxes separate if possible and voila! Question: Why not (also) let your breeds intermingle and select the best hybrid varieties? You could wind up with the perfect breed for you if you select long enough.

I want to be able to breed by my choice, at least until I get a better understanding of breeding. Also I've got some Black Java's which are a threatened breed and want to at least breed them true to type even if I cross the black java rooster with something else.

While I'm not breeding I want to keep them all together in a mixed flock just to make my life easier.

Back when I was in 4H I was told one month of separation before saving eggs for hatching.