The standard new-bird quarantine procedure is the first 30-days in a completely different room, and if possible it's best to keep the new bird behind a closed door. The new bird can absolutely not be in the same room as your current bird(s), as they would be sharing the same air-space, and if the new bird that you bring home were to have any type of Avian virus, bacterial infection, fungal infection, etc. that is airborne (most are), your current, healthy birds will most-definitely contract them.
The reason it must be at least a full 30-days is because of how long the incubation periods for most Avian viruses is, along with the fact that birds hide all outward signs of illness for as long as they can, and it will take at least that long for you to be able to tell that something is wrong with your new bird. There are many different new-bird quarantine protocols that call for more time and different procedures after the 30-day period as well. For example, you might near "The new bird must be kept in a totally separate room, behind a closed door for the first 30-days in the home, and then after the first 30-days you can move them into another room without a closed door, but still not in the same room as your current birds until they hit 45 days, and then you cannot let them be out of their cages together until 60 days has gone by", etc. But the standard new-bird quarantine and the very least you need to do is to keep any new bird that you might bring home in a totally different room from your current bird(s) for 30-days behind a closed door to segregate the new bird's airspace.