I just finished building a small coop and run for my seven 5 1/2 week old chicks on Sunday. It has been unusually warm the past couple of days (60+) but it is going to start to cool down after tomorrow. The past few days has been their first time outdoors ever. At what daytime temps should I keep them locked in the coop? For example is below 45 OK or not OK for them to have an open pop door at this age? They appear to be fully feathered.