Mine get their own at about 4 days or so. I get a big clump of sod from the yard - grass, weeds, tiny rocks, sand, roots, bugs and all - and put it grass side down in the brooder. At first they’re terrified of this huge alien in their space but soon one pops out from under Mama Heating Pad to investigate. Before too long they’re all over there, pecking, scratching, playing King of the Mountain on top, and getting bits of natural chick-sized grit and exposure to the pathogens and fungi that will be present in the soil when they go out. As it breaks down they love to dust bathe in it.
I raise my chicks outdoors from the start, and try to do it as closely to a Mother Broody as possible, from their heat source to their natural day/night cycles and diet. Yes, even out there they get their clump of sod, if the ground has any thawed patches. If you think about it, 4 days is about the time she’d have them out of the nest and in their full time environment. They'd be eating everything from chicken poop (yes, they do that and it helps build immunities) to bugs, seeds, grass, weeds, and whatever else Mom calls them to try. They drink out of mud puddles and standing water from rain or garden hoses. I try to duplicate all of that. At 2 weeks they are mingling with the flock, at 3 they are spending every entire day with them, and they are totally integrated by 4 weeks, at which time their brooder is totally removed.
