It takes 25 hours for an egg to make its way through the chickens internal egg laying factory. The egg can only be fertilized during the first 15 minutes of this process. If a rooster mates with a hen on Monday about the time that Tuesday's egg has started its journey through the hens egg laying factory, Monday's egg will not be fertile. Tuesday's egg will not be fertile. Wednesday's egg will probably be fertile. If the mating occurs early Monday and Tuesday's egg is laid late on Tuesday, it is possible Tuesday's egg will be fertile, depending on the time of mating and the time the egg starts its journey through the hen.
After a rooster mates with a hen, the hen will probably lay fertile eggs for 10 to 14 days, even if she does not mate with a rooster again. Sometimes it is less and sometimes it is more, but the average is around 10 to 14 days. 3-1/2 weeks is the latest I have seen reported on this forum.
A rooster does not necessarily mate with every hen in the flock every day. Just because a rooster has been with your flock for a few days does not mean that all eggs are fertile.
I'd be pretty confident the eggs would be fertile from 3 to 14 days after a mating. After that, I believe your chances of fertile eggs drop off. I understand breeders usually wait three weeks after a certain rooster has been removed from the hen to be pretty certain he is not the father.