If they are in a run... you can start as soon as you take them out to the coop, just place them in the coop for the first few nights until they get the idea that is where you want them to stay at night. If you are talking about completely free range (no walls/fencing) I would leave them in the coop for about a week so they get the idea to sleep here, you may still have to round them up a few times after you start letting them out during the day (I always lock my chickens up at night- even those that free range). But personally i wouldn't allow them to free range until they are almost fully grown, but we have alot of predators in our area. Right now my 9 week old have a temporary run, eventually they will have acess to the property!