Mine were just shy for 4 weeks when I put them out with the silkies. The 3 Marans were still fluffy, but they had the other 7 older chicks to keep them warm. They  have been out for a week, and Sat & Sun. it rained, they were out in the rain & were fine. No heat lamp, they just puppy pile in the corner of the coop at bedtime. And it only took them 3 days to learn to put themselves to bed!
 
3 New Hamp, 2 Black Aust. 1 Frizzle & 1 Bantie, 1 week younger are 3 Marans Got the forst set on Feb. 2nd, the other 3 on Feb. 11th.
 
They should do fine.