The answer to how long the quarantine lasts completely depends on how long area birds are testing positive. When California was fighting VND, it was a "good while" before Any birds could be brought into the quarrantined areas, including day old chicks shipped from hatcheries. (The exact time frame can likely be found online; I didn't follow the issue That closely.)
There is probably also quarrantine info online from 2015 when Avian Influenza ravaged commercial egg farms. The current outbreak isn't the first, & it won't be the last. I kept tabs on the situations back then as I am doing currently. The issue isn't something to obsess over, but to be aware of and take immediate action if the disease shows up in your area. If such diseases ever occur in my area, I will be able to state Exactly how long quarantine lasted, how many birds died, etc etc.
Personally, if influenza is found near my area, I will be confining my birds until the all-clear is given. My runs and coops are completely wrapped in 1/2" hardware cloth and covered with metal roofing. I did that to protect against against woodland predators, but it will suffice to protect against Avian diseases too. Yeah the hens will be upset for a while over being jailed, but at least they will live. (Hopefully.) Avian Influenza is mostly asymptomatic in wild waterfowl, but has a high death rate in poultry. Meaning if a flock contracts it, yes the entire flock will be depopulated, but many will likely die of the disease anyway.