Proper quarantine is at least a month and FAR away from the existing birds. Here is a good article about bringing in new birds.
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/
It is important to properly quarantine in case the new ones have hidden illnesses that the stress of moving will cause to flare up.
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/
It is important to properly quarantine in case the new ones have hidden illnesses that the stress of moving will cause to flare up.