when we brought goofy home, his quarantine lasted all of 2 weeks. while he hadn't been vetted, he was a healthy bird. but i didn't bring him into our family after a short quarantine without some anxiety. but i had guests, and one of them was a mouthy young boy, so in goof's best interest down he came when they got here.
zuzu got a full month. not because i worried about his health or possible issues, but because since he's the same species as louie and we intended to introduce them physically at some point, i wanted to do it right. they called to each other for a month before seeing each other. it was a VERY long month

we have a 2 story house and kept the new birds in the computer room upstairs, while the existing flock lives downstairs. we also took turns. i would send the girl up to hang out for a while, while i hung out with louie (and goofy, later). then she would change clothes and we would switch until bedtime. ian would stop in for a few minutes, but he didn't spend a chunk of time with zuzu like the girl and i did, and i honestly think that's why i had a better relationship with him initially. he's more social with ian now that he's been here a while and settled in.
i think quarantine is necessary not only for protecting your current flock's health from possible disease, but it also allows you to bond with your new bird without the interruption of a jealous bird or other fid distractions. it's a get to know you period that is essential, in my opinion. i got a lot of bites from zuzu once he got comfortable enough to come out of his cage (and admittedly i did kind of push him to step up and stuff, probably sooner than he was comfortable with), but we also go to hang out in the girl's bedroom, one on one, and i could handle him. we learned to trust each other, and that made his integration into the flock a little easier i think.
kris