When to start free ranging?

[MegaChickens]

I have a few new chicks for this season and they have been staying in the coop and run, but when can I safely allow them to free range with the older chickens? The new ones are still a little small but they are feathered out and are doing well outside. Also how long should they stay in the coop so that they know to come back at night like the older ones do?

 

[Mattemma]

I did not add my 6 EE pullets to the older 3 RSL hens until the pullets were about 16-18 weeks old.

I had them outside in a run next to the older hens run,so they could check each other out,but there was no risk of the older hens pecking the younger ones. Also, both groups had bird netting over their runs,and I was always close by. My yard is fenced with chainlink to reduce the risk from roamer dogs,but the risk from hawks is always present.