also too, when a roo mates and "fertilizes" the hen, won't she lay fertile eggs for a few days without another mating session??
so you may have an extra day or two once the roo is gone, of fertile eggs, if this statement is true that is.
also, isn't there a way to stall the development of the egg for a few days (like keeping it cool or something?) I don't know much about all this yet, I am just starting to encourage a broody in my flock, and already considering making a bator just in case no one is interested in setting on them naturally.
good luck! I hope you get the answers and help you need