I have had chickens on and off for over 40 years. At one time I had over a hundred layers that get me quite busy. But I have never raised bantams. At three and a half weeks old, they are almost completely feathered out and they don't seem to enjoy the brooder heater as much. They are quite Lively and some of them are even flying in the brooder. My question is, how soon will they be ready to go outside and take the cooler weather?