I'm not a expert but I wait until they start laying so they would know that is where they need to come back to lay. Also because I wanted them to have a strong start with the chick grower feed and not fill up on whatever they forge. I did let them out supervised when they were fully feathered for a few hours at a time but not out and about by themselves until laying.
If They were hatched by a hen then I would have let her guide them and do what chickens do.
a broody will have them out at 2 days old. So if you have a broody, let them out now. If not, you need to provide them with some heat source until they are fully feathered (about 6 weeks), so could go out for a bit if it's pleasantly warm out where you are. From 6 weeks they should be fine outside as long as your temps are not extreme.
Answers are going to depend on lots of factors. In our case, we have an older established flock that free ranges a few hours a day before dusk. First we integrated the younger birds with the older flock in a large fenced run for a week or so, then we turned them all out to free range together. The young birds did a fair job of following the older flock back into the run for the first few days. (They didn't go far.) Some of them got confused and we had to help some of them find the gate. After a week they were all doing great. They were about 10 weeks old when we started integrating, so about 13 - 14 when they started free ranging, as I recall. Hmm. Maybe I should keep notes on this stuff! They are 16 weeks old now and I'm starting to look for eggs!