As the old joke went
"I hear you are taking up breeding chickens. I didn't know you knew anything about it."
"I don't! But the chickens do!"

Having said that the hens will decide when he is acceptable, there may be a bit of squawking and running about till then, but they'll sort themselves out. If you haven't many hens, and he is particularly enthusiastic, or a very heavy breed he may eventually wear out the feathers on their backs. You can buy ready made poultry saddles, or only put the cockerel in a couple of days a week. The hens have "sperm nests" in their oviducts and eggs can be fertilized for upto 2-3 weeks after a mating
All the best Sue