Yup, 12 minutes is right. Not only that, but that's how long you've got to kill the real Ubel. I happened to ***** up once and pulled the avatar before anyone had hailed him, so there was nobody ready to loot the amulet off the real Ubel, so we just let him live. At exactly 12 minutes after the avatar died, the real Ubel despawned as a fresh avatar appeared.
-845, -760 is his Loc.. He spawns a mob Adriane Ubel (the real version is lvl 84 or 85). Both are kiteable.. snareable.. rootable. easy kill. 81 druid soloed him. Is part of Destroy the Imposter Quest.