Scion/Zion is haunted by visions of his own death. For each time this drawback is taken, it half as much time for Zion to initiate Golden Morning until something sets him off (counting from the moment of your arrival). It could be that Jack gets the idea to influence him early, Zion realizes that humans are using the remains of his dead partner to create more Parahumans, or any number of other things. Now you are locked in, and nothing can change Zion. Even if you kill Jack Slash before he sets off Zion, he will still initiate Gold Morning after the correct amount of time has passed.
If taken on an Alternate Earth this instead changes the local doomsday scenario such as The Snap (MCU), The Reapers harvest of the universe(Mass Effect), or Voldemort's return and subsequent fall of Hogwarts(Harry Potter).
If there's no existential threat present at all, a random one will appear and will act up in about a decade.