A quarantine period of only a few days would be useless to achieve anything except reduce the stress of the bird for a few days before entering your main flock. Correct quarantine procedures require you to initially identify the diseases you want to keep out, then should be structured to achieve this. Remember, not all diseases can always be avoided and kept out. Some of the viruses can have long incubation periods and remain dormant for long periods.
With my Zebras I try to keep out parasites mostly, as well as any obvious diseases. To prevent parasites one must treat the birds at least twice whilst in your quarantine area with a reliable drench (wormer) as well as reliable external parasite control. These two treatments should be 3-4 weeks apart. The first will kill any adult parasites but juveniles are always resistant and the 3-4 week gap allows them to mature for treatment but not enough to breed (hopefully). Your birds must stay in quarantine for this whole period and at least 1 week after to allow any worm eggs left in the intestinal tract to pass. The ideal cage structure for quarantine is the suspended (all wire floor) cage as this helps prevent reinfestation.
Any new Zebras that enter my establishment are also housed separately to my main aviaries up until they have been used for breeding. This serves two purposes. Firstly, the stress of breeding will bring out dormant illness, allowing their identification and culling and control before contaminating your whole flock. Secondly, often the biggest risk to new birds is stress weakening them and allowing the endemic diseases in our own flocks to kill the new birds. All flocks have diseases that our own birds have natural resistance to. The new birds need time to regain that resistance. Any young bred from the new birds will adapt to your methods and environment, so they should not have major problems.
With my parrots, I quarantine for at least 7 weeks. The reason being that I try to prevent Chlamydia from entering my yard and seven weeks is the minimum period of treatment for this disease. All parrots have weekly long acting doxycycline injections for 7 shots as well, and worming twice with levamisole and treatment for external parasites with frontline topspot at least twice.
This might seem extreme to many, but if you truly wish to prevent disease rather than just ride your luck, then you need a full program in a structured manner like those I have just described. Alternatively, keep the birds a couple of days to acclimatise then cross your fingers.