Sperm can last up to three weeks. I've tried it this year using a rose combed male on single combed femlaes that had been running with a single combed male and I was getting some single combed chicks at 19 days.
Some were rose combed during the three week period too. So to be safe, if you want to be sure of the parentage of the chicks, allow three weeks after the new male has been introduced.
If the hens have not been with a male, eggs can be collected two days after the male is introduced as long as he treads them straight away. Some males take a little longer to get mating. I've tried this this year too and tested eggs at five days that were laid two days after the first mating.
