What is the least amount of time to seperate breeds before hatching?

Ok, don't give me a hard time on this one, I just need to know.

What is the correct amount of time to be SURE your hens are fertilized by the roo in a breeding pen, and ONLY the roo in the breeding pen, after you separate them from a mixed flock?

I run most of our breeds in a huge (2+ acre) pen or totally free range most of the year. I just like the idea of them being free range and it's a heck of a lot easier to fill just a few large feeders every day than to fill 30 small ones, plus when they are running loose I fill water troughs up by the barn and they have the pond to drink from instead of all those individual waterers. I have always separated the breeders of each breed I was going to raise from into breeder pens on January 1st each year and started collecting eggs to hatch out on March 1st. That's two months in the breeder pen before hatching any eggs from that breed. Any eggs laid before then are just ate or sold as eating eggs. I've never sold hatching eggs, just hatched out my own replacement stock (I do give a few hatching eggs away if anyone asks, but it's been rare as most people around here prefer started birds).

My thing is that this next year I would like to start hatching a bit earlier in the year, but as of now most of our flock is still free ranging. I've researched it and the numbers are all over the place - from a week up to three months! I'm confused! What do those of you in the same situation think is enough time?

Nothing against mutts, but I've got plenty of those without raising more.

 

Thanks Silkiechicken! That's what I was needing to know!

 

Thanks everybody. Looks like four weeks it is!

Now to get them all caught.