I put mine out in Alaska sun yesterday. They were still in the brooder bucket. It did seem to encourage flight activity so now I have had to make them a second brooder in a wire dog kennel. I have placed it in a sunny window and now they sun themselves in the sun instead of under the heat lamp. They are MUCH louder and messier now.
The impression I've gotten is that chicks are, in fact, not completely vulnerable to chills. The problem is that they eventually get cold and then need to go someplace warm to heat back up. If they were being mothered by a hen, you'd see days old chicks running around like ping pong balls in 50 degree weather. They'd get cold and then run to mama to warm up under her skirts, and then back out into the world for more silly chick games It seems very likely that week old chicks are perfectly capable of being outside in the sun and surviving the experience. But that is assuming that you are there to make sure they can get or are brought back to warmth before they get chilled.