Two issues pop to mind for me: openings and context.
You mention that the two stories are in the same story world; I’m not sure if that means they appear in the same novel, or if you’re talking about two separate books.
In either case, without being familiar with the context of your stories, it’s not possible to decide which one needs your more immediate attention. Remember that stories need escalation of conflict and tension, so, if one of the stories builds up to a more intense climax, that one should come last, chronologically. You always want to save the best for last, the plot must always thicken, never thin.
I’m not sure if Tolstoy actually said this, but there’s a story in writing circles that he once said, “The first thing they read is the last thing you write.” Here’s the point: You’ll only know how a story needs to begin when you know how it ends. If it ends with a person deciding to move from Cincinnati to LA, you know that, at the beginning, this has to be their struggle. So, when you get done, you would go back and recast the beginning so that it is tied in inextricably to the end of the story.
Too many writers spend inordinate amounts of time on their openings, their hooks and so on. They go to “first page critiques” sessions with other writers and bring their work to their local writers groups and keep polishing something that they might not even use in the end. Instead, it’s vital that we work through our stories, flesh them out, see where they lead, and then, once we know where they’re going, head back to the beginning and start them off aiming in that direction.
Whichever story you decide to develop first, let it inform your work on the other story—whether that involves making promises and foreshadowing (if you write the one that comes 3000 years before the other), or if it means fulfilling your promises (if you write the later story first).
Finally, I would suggest that you follow your passion. You might be more excited about one or the other. I’d go with that one. Let that give you momentum and fuel for the long hours of writing you will undoubtedly need.