I am a big fan of integrating early. I have raised the last two batches of chicks from day 1 in a coop brooder. The first group were let loose with escape doors at 5 weeks & the present ones at 4 1/2 weeks. They just turned 8 weeks old & they have been on the roosts with the big girls since 6 weeks. It has worked like a charm both times after 25+ of doing it the other way.