If a sexually active rooster is placed into a flock of hens, fertile eggs can be produced by the second day after introducing the rooster. If mating occurs within a short period, the next egg yolk released by the hen's body can be fertilized. The remainder of the albumen and shell requires about 26-28 hours to be formed around the fertilized yolk. Therefore, a minimum of 30-36 hours is necessary to produce a hatchable egg.

If the flock has many hens and only one rooster, it may require several days before mating with all hens takes place. It is advisable to allow at least 4-7 days before expecting a high level of fertility in eggs. If the rooster or hens are one-year or more in age, the waiting period may need to be increased.