They look feathered out pretty well. As long as there's a draft free spot for them, it should be fine with those temps. If it's below freezing when I move chicks outside, I just set up the heat plate so they can warm up a bit, if needed. If your coop doesn't have electric, you can always run an extension cord to plug in the heat plate. If you're using a heat lamp, just be careful. If it gets knocked over, it can start a fire quickly. You can always put a box, sideways, on the coop floor for them to snuggle up into on cold nights.