New chickens in isolation, questions

Yesterday I picked up 3 new chickens. I currently have them separated from my other ones. My main flock is free ranged during the day and get locked up at night. The new chickens are in the pen next door (w/ a wall between the two) to my already existing flock. Is this to close of quarters for the new chickens to my existing flock? As I stated the existing flock free ranges during the day so they are not in the coop at all during the day, only at night. I only have 2 chickens that come into the coop during the day to lay there eggs and then they leave after they have laid. The coop really isn't a coop as it was originally built for parrots. So there are small area's next to one another separated obviously w/ walls.,

The other question I have is I have an area in the back of the coop that is open. and am wondering w/ the new chickens if it's ok to let them in that back area during the day so they don't have to stay locked up 24/7 until I introduce them to the others. I have that back area closed off so my other chickens can't get to that area.

Finally, how long should I keep these new ones separated?

Thanks