So last night while harvesting in thulumbra for arcannium, I spawned a fowlumbra zone and went duck hunting. Lol. How long is this event? It was nice making some easy plat on test server.
It's not an event. It's the "hidden zone" of the ToT expansion. There is a similar zone for KA. I don't think anyone, outside of DBG employees, knows what triggers the zone. I think the zones are limited to once per character.
ToT duck portal is spawned by killing random mobs in Thalumbra (portal will pop on mob's corpse), only the toon spawning the portal can zone in. You do not need to have done the ToT questline to trigger it. After someone zone into Fowlumbra, there's a 12h "cooldown" (at least back then, this might have been reduced since ToT) with no portal. If someone pop the portal but doesn't zone in, there will be no new portal until the 1st one depop (not sure how long, 1h or less)
I have never been lucky enough to spawn this portal and I have spent a ton of time harvesting and killing things in Thalumbra. Congratulations!!
It's at least once every 24h, not sure for the 12h mark, as I was able to spawn the zone at roughly the same hour 2 days in a row. It is once per char.