You can keep them in the pen 24/7 after they don't need a heat lamp anymore. I move my meat birds to their pasture pens after three weeks in the brooder.
bigbluehen53: I totally understand the concern with the density, but meat birds in pasture pens (aka "chicken tractors") have much different requirements for space. They need less space because they move less, but at the same time, they need to be moved often to keep them off their poop. We raise our freedom rangers in 100sqft pens with 65 birds each. So our density is about 1.5 sqft per bird and that is a much much lower density than alot of production farmers that are using similar pens. They have never seemed crowded to me and 9 times out of 10 we have a very successful batch.
Thank you also for explaining that. I am here to learn so I appreciate you and @RUNuts taking the time.