Hi Ladygirl,
The chicks can go outside as soon as you'd like them to, as long as they have enough heat. If you're interested in how and when I moved mine out to the coop, you can check out my blog (link is below in my signature) and start reading at the post titled "the Big Move." I moved mine out there when they were two weeks old and they liked it much better than being in the brooder. However, I provided them with two 250 watt heat lamps because it was still getting into the high 20s/low 30s at night. I took them down to one heat lamp at 8 weeks and no heat lamps at 10 weeks.
I my reading, I have learned that they are generally fully feathered out at about 8 weeks old. At that time, they can handle 30 degrees without supplemental heat. I left one lamp in there another 2 weeks because some of them still liked it, though they didn't need it. at 10 weeks, they all stopped using it so I took it out.
Anyway, point is... they will be fine outside at 2 weeks old or older as long as the coop is very secure and they have the heat they need (90 degrees week one, 85 week two, minus 5 degrees each week to 8 weeks). Those are the temps they need directly under the light... cooler as they walk away from the lamps. They will fine their comfortable temps.
Good luck to you!
