Mr Longbeard, I could be wrong , but as I've understood a Hen can Lay eggs at any time even with out being mated, The thing in consideration is whether the egg is fertal or not. Now again I'm not 100% on this either but I heard it takes about 48 hours for a hen to be able to fertal eggs.
A hen system can save sperm of a gobbler , untill she is ready to set. If at some reason she is invated from the nest, she can again lay a fertal clutch without mating again...BT