Parallel world of Draenor.
Boss Hu did not want to kill Meng De ahead of time. As for the timeline he had personally experienced, he believed it was best to leave it as it was and not alter it recklessly.
If he personally changed and completed something he was supposed to do in the future thirty-five years early in the parallel world of Draenor, and accidentally caused some kind of time paradox, that would be quite the mess.
Timelines and the flow of time were complicated and mysterious things. Boss Hu was no god of wisdom, so he could not be bothered to understand them. While he could freely alter the fated destinies of certain people and events, changing his own timeline and things he himself had done would bring entirely different consequences.
To give a very simple example, if Boss Hu suddenly went feral and killed Meng De now, then the Battle of Mount Hyjal from back then would cease to exist. And if the Battle of Mount Hyjal did not exist, then the World of Azeroth from thirty-five years ago would also be changed along with it.
Boss Hu did not want to risk finding out what effect that would have on the current World of Azeroth.
"Your doom is at hand! Azeroth, you pitiful world, will soon be burned to ashes by me! The Burning Legion shall triumph! Hahahahahahaha—urk!"
Archimonde's enormous blue body strode toward the Dark Portal, while countless Legion demon soldiers served as the vanguard clearing the way.
To Archimonde the Defiler, this damned parallel world of Draenor was nothing. Only the World of Azeroth was the true target. He had to destroy it with his own hands to avenge old grudges.
Yet strangely enough, the road leading toward the Dark Portal was completely unobstructed.