They start at 00:00 GMT (Midnight) on the first Wednesday of every month. The spawns continue for one week. What zone it is in varies each month. Best times to fight World Bosses tend to be during EU primetime. Just ask in Global chat during that week for where the World Boss is currently spawning and someone will point you in the right direction.
The bosses spawn on an approximately 25-60 minute timer which starts the moment the boss dies in each instance.
1 Like