I start letting my chicks out when they are two weeks old, at first with constant supervision and then less and less supervision as they grow and "learn the ropes". By about 10 weeks old they are staying out all day and I check on them several times a day.
My adult flock has been free ranging since they were at that two week old period. I let them out in the morning and lock them up at night. I go out a couple of times a day to check their water and collect eggs. All my hens lay in the coop. I've seen them run across fields to make it back to the coop in time to lay.
I can sit in the house with the air conditioner on and still hear if there is trouble. Ordinary chicken noises - egg songs, rooster crowing - I've learned to ignore. My rooster can make certain noises, alarm calls, that get me out there in a hurry. GET A GOOD ROOSTER.
It's my opinion that the younger you start free ranging the better equipped the chickens are to take care of themselves. They learn about predators, when to hide (hawk overhead for example) and what they can ignore (crows or other non-threatening birds). In the oppressive heat we are having right now, my adult flock goes to the woods and that's where they stay for the majority of the day. I wish my baby flock were old enough to follow them. They'd be much better off.
Most, but not all, of the predators we have around here are nighttime predators. My flocks are locked up tight at night.
