It doesnt matter if they are hatchery birds. Some hatchery birds are very nice. You just have to be careful where your getting them. I will only buy from one particular hatchery because I know where they get there eggs from. But back to your question. The best way to explain it is that young birds go thru a learning process. The cockerel has to learn what to do and the pullet has to learn what to let the cockerel do. It takes them time to start laying and just plain simple learn what reproducing is all about. Im not saying every bird is like that. We have some birds like my Sussex who I have hatched off of 1 month after they started laying and have had right at 100% hatch. Others like my Blue Orpingtons I couldnt hatch off of until they was around 10 months old. It varies from chicken to chicken. There is alot out there on the net to read. If I give anyone adivice or my opinion is is from the experience Iahve had inthe past. I guess at nothing, If I dont know I will tell you. I always recommend waiting until the birds are 10-12 months old before hatchign off of them unless it is a rare breed. Then people will hatch and lose what they do in order to get the ones that hatch. In the past with young hens we have had the most abnormal chicks, chicks with various problems. That why I dont recommend using young birds less than 12 months old. A female is not a Hen until she turns 12 months old. You will hear not to hatch a pullet's eggs on the internet. That is what they are talking about. If you have anymore questions feel free to email me or message me. I dont mind to help anyone out.
