To answer your questions:

1. It depends on the individual hens. According to Monroe Babcock, creator of the Babcock B2000 commercial egg layer, the’s ability to maintain an environment conducive to keeping the male’s semen alive varies, and is linked to the hen’s reproductive performance. In some hens, as little as 3 days. In other hens a week. A few exceptional hens have been viable for up to 3 weeks but this is more rare. If it were me, I would save and set eggs until fertility ended. But make sure no other rooster mates these hens… see below.

2. When is a hen fertile from a given rooster. I realize at the end of question 1 you asked this, but it is also the basis of question 2, so I have combined them. If you want to know positively the sire of a given mating, a hen should be pared with that male for 2 weeks prior to egg collection. But Dutch studies show that once a hen has mated with a male the eggs will be fertile from him and not a previous male beginning on 3 days. Now there is a catch. Hens can and do perform exclusion – in other words they have the ability to at least partially exclude the semen from a low ranking male (male they do not see as a suitable mate). So if a hen preferred one male, but you preferred the second male, there is a good chance the eggs laid on day 3 and beyond will be fertile from the first male. If she sees both as suitable, usually beginning on day 4 or 5 and beyond only the second male will be the sire. But best things is to give it one to two weeks before collecting eggs.