I did 1 hatch earlier and put them out I think at 2 weeks. They were stinky. But they are PROTECTED from RAIN with a large covered Roof. The only way rain could get to them is if we had a Tropical Storm come through. They have a LIGHT on at night or when the temp starts to drop below 85 degrees or so. They also need to be protected from WIND.
It really depends on how you are set up for them. This hatch of mine, will be in the house for 10-14 days. Actually all my hatched chicks, chickens or quail go out at 10-14 days old. If its not raining, out they will go. I won't bring any chick out when it's raining, no matter what DH says. I waite for a nice day, weather wise, and I have waited over 3 weeks in the past. DH was not happy. I hatch frequently though and can hatch throughout the year, so I can take a chance on loosing a hatch. It hasn't happened to me. But it can anytime.
Most people waite until they are feathered. If you are not set up to put out younger chicks, you should waite until their feathers are in. And watch the weather forecast. I do.