Depends on your coop, are they sharing a coop, do you have a tractor or free ranging them. temperature outside and are they feathered out.
I live in Florida and I have a coop I can place my biddies so that no one will bother them. I have a run that is not covered and we have cats so I learned the hard way that the cats will chase the pullets under 5 weeks and hunt them. Not so good for me. If the temperatures range in the 80's I will move them out of the house into the outside brooder during week 2 but they don't get to go into the run loose until week 5 or 6 because they have to be big enough for the cats to leave them alone. My cats actually have slept with the chickens in the nest box and the chickens can care less. The cats rid the coops of mice and snakes so usually it is a win win for me.
I have an enclosed coop with a tractor. Originally, I used that for the chicks and moved them into that at 4 weeks. It is hotter here in Florida so if they can be warm enough then I am all for taking them out. If the weather is cooler - wait for them to feather out. Some breeds take longer than others to mature.
I would not put biddies in a run with older chickens because they will pick on the little ones. The biddies need hiding places. Wait until they are closer in size.
we plan to build our coop (based on Wichita cabin) ourselves and have ready for the time needed when the flock can go out into it.
6 hens is our initial goal. local supplier here in Albuquerque says late Feb./early March they will have chicks.
So again, i'm planning to have them in an indoor brooder from day one of getting them - they stay indoors how many weeks ? you said once they're feathered ? how many weeks is that approx. ? we plan on 6 different types of hens too.