We found having a light in the coop at night on a timer helps them to know it's a safe place in the coop when it gets dark out. I think they find it kinda scary to walk into a dark coop when it's dark outside, to them they don't know if something is hiding in there to get them. Ours were about 6 weeks old when they put themselves to bed, they we just close the coop door before we go to bed.