I kept my new chicks -quarantined for 12 weeks. Then moved them into a separte area in the coop for a week and then into a fenced off area of the run.. It was not just for illness, I was waiing for them to get some size on them before I put them in w/ the big girls..
The 14 week olds were quarantined for 35days.. During this time I handled them, and listened to each on breath--listening for any thing different, I watched for runny noses or anything that might sound/look like a cold.. I wormed them and dusted them for mites/pests..
I have almost 100 acres -so you would think keeping them separated would not be a problem...WELL, I let my girls free range, came in for about 30 min.. and found them over 150ft away Around the quarantine coop! Thank goodness, I ended up w/ healthy birds or I could have lost my org. 5 girls and I would have been really sad! So, where ever you have them be sure that your org birds can't wonder over to them..