In King’s world, all timelines serve a greater power called The Beam, and all beams lead to The Dark Tower, so as long as all characters stay on The Beam, that’s what we can expect in the movies.
When Is The Dark Tower Set?
But for now, it’s safe to assume that the bulk of The Dark Tower will take place in Roland’s home of Mid-World, in an alternate and futuristic timeline, with occasional pit stops to familiar locations on our own timeline.
Stephen King primarily sets his Dark Tower stories in Mid-World, which exists in an alternate (and assumedly future) timeline that might run parallel to our own.