I’ll answer something you did not ask but it might be good to know, then I’ll get to your question.
It takes about 25 hours for an egg to go through the hen’s internal egg making factory. That egg can only be fertilized during the first few minutes of that journey. That means if a mating takes place on Monday, Monday’s egg is certainly not fertile. Tuesday’s egg might be but I would not count on it. Wednesday’s egg will be. This is after a successful mating, not just introducing the rooster to your hen.
The last part of the mating ritual is that the hen stands up, fluffs up, and shakes. This fluffy shake puts the rooster’s sperm in a special container near where the egg starts its journey. We normally count on that sperm remaining viable for about two weeks after a mating, but it can last longer. Many breeders count on a three week wait before they consider a hen cleaned out but there have been some cases where the sperm has remained viable for longer than that. So if you want to be as sure as you can reasonably be, wait four weeks.
Of course nothing with chickens is that simple. That container that holds the sperm acts on a last-in first-out basis. That means the last rooster to mate with the hen is almost certainly going to be the one that fertilizes the egg. The other rooster still has viable sperm down in that container so this is not going to always be 100% sure, but if your flock is small enough that the rooster mates with every hen pretty regularly it is reasonably safe. This is probably why breeders that wait only three weeks are pretty successful not waiting four weeks.
Nothing more can ever be added after Ridgerunner comments
I give them 3 weeks to be sure. I ended up with some funky naked neck/houdan crosses when I waited only two weeks.