I've read not to let them out til two hours after dawn because of predators. If I am out there with them, while not a guarantee, I don't mind letting them out within an hour of dawn.
Also depends on if it is really hot already.
Sometimes, if the weather is cooler, they might get let out three hours after dawn but that's unusual. I would say they're locked up between 9-12 hours but free ranging the rest unless it's raining. And even then we might trust some of the bigger birds because there's lots of cover. Just the silkies and the little ones have no preservation to stay dry.