Many variables but here is what we do. We wait until at least 3 months or more before they hit the ground. Even at 3 months, if the weather is tooo cold, they can suffer. We move them from small brrooder boxes to bigger ones as they grow. Silkies are beautiful but also frail and delicate Underneath all that fluff is a very small body, that is very susceptable to drafts and rain, winds, snow and ice. The longer I can wait the better.
editing to say that our Mobile tractors have no Heat source and that is a large part of the reason we wait. Thought I had said that, sorry. Even as I type, in about 30 minutes, I'm going to go out and wrap more of our chicken coops. Temp again is key.