I open the door and let mine decide what they want to do. They have plenty of cover outside of the coop, so they can choose. There's not much that keeps them in- even the first time we had snow, they came out cautiously and were all running around in it a few minutes later. They didn't like it (you could see them thinking, "What the heck is this stuff?"), but their desire to go outside was more powerful than their dislike. I say as long as they are fully feathered, let 'em out.