I have 7 week old chicks and am planning to have them in an electric fence run when they're adults. I have them in the coop now and am wondering at what age I can start opening the coop up and letting them have the option to come and go into that fenced area/coop all day? I would like to start giving them some time out there each day when possible. It's in the 70's at least, so temperature is no issue.