The guildhall portal resets as soon as the instance of the guildhall is closed, sometimes after a view minutes. Since the last patch, the guildhall-portal remained open to the set location for about 6h, no difference if a guildie parked a char in the guildhall to keep the instance running or not. After the last patch, the guildhall-portal is reset as soon as the instance is shut down.
The last patch fixed a bug where guild halls would sometimes not close. This is why the teleporter was not resetting. It is fixed now (it's bad to have a zillion guild halls running).
