hmm, my Scots Greys can start crowing at 9-11 weeks but have not seen any tread until they were 18+ weeks old!
I never used to split them, never had any problems with cranky cockerels. Split them the last two years and ended up culling some nice ones that turned into gits. So this year I am not splitting-they will all run together until the spring-although I am only keeping two males from this years growers, to join one other adult male later this summer.