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If you got the birds directly from a hatchery or someone with a NPIP flock, and you have checked them to be sure there are no respiratory problems, mites or other obvious problems, I would just quarantine them for a few days to be sure they are settled into your environment before adding the stress to them of meeting new chickens and establishing the pecking order.
If the new birds began as hatchery stock but have been living somewhere other than a hatchery for the past 9-10 weeks, I would give them a little longer on the quarantine, since they may have been exposed to something since they left the hatchery.
coming from a hatchery originally doesn't mean that the birds are any healthier than birds acquired from an individual nor does it automatically mean that they have had any immunizations. It does however mean that (theoretically) that they started out healthy.