How long have you had the newest 3 Guineas? Is there any fighting/pecking between the caged birds and your existing flock? If so you want to wait until that's not going on any more, because if you do let them loose together the 3 new birds may get chased off and you'll never see them again. If they seem to be getting along while separated by the cage you could try letting them integrate in the coop a few times first and see how it goes, but if it's a small coop that could back fire on you (and the new birds)resulting in too much aggression from the existing flock, in a small space. It could get ugly, so be sure to supervise.
The full 6 weeks acclimates them to a new home and also lets everybody get used to each other... but they need to be able see each other and be near each other as much as possible... just mornings and evenings isn't really going to help them integrate into the flock quickly. Do you have a decent sized cage you can safely set the 3 new birds up in during the day outside the coop so they can see the free ranging flock and vice versa? That would help a lot and also let the new 3 bird get used to the sights and sounds of your property.
Since there are only 3 new birds, they may bond to your flock and new home quicker than 6 wks... but without a covered run and plenty of time to acclimate to integrating you might have some issues getting the birds to coop up each night... they won't want to go into a coop they will get beat up in, if they even stick around. It really depends on how aggressive your flock is towards them, and how flock oriented the other 3 are... they may want flock security (most do), but they may not, and they may go looking for their previous flock especially if your flock is aggressive towards them.
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