I have a question about egg laying feed in chickens?

I have 6 chicks that are only 4 weeks old, so I won't have to worry about it for a while, but I was wondering, if one chicken starts laying early, do I switch them all over to layer feed? if one say starts laying 1 month early, will it harm the other chickens to start on layer ration if they don't start laying for a month? thanks!