Time would have passed at a "slower" rate relative to a hypothetical "earthbound" observer.
I'm a little confused. Are you saying that this hypothetical observer would have aged 6000 years, while the earth beneath his feet would have aged 4.5 billion years?
"Relative" to his frame of reference, yes. But that phrase "frame of reference" is the fly in the ointment as being part of it we can only "observe" from within the universe.
Though perhaps hopefully for example, conditions on the Sun take place at a "slower" rate than here on Earth owing to it's larger gravitational field. And events on Earth pass more slowly - albeit microscopically - than events on the Moon.
What's interesting is that from our perspective, it takes a photon about 8 1/2 minutes to transit from the Sun to Earth. Yet if we could ride the photon, moving at light speed (which is "equivalent" to a gravitational field approaching infinity [the mathematical "limit"]), we would experience no transit time at all.
This bears on the "quantum" nature of light, which opens the door to so called "quantum weirdness" by which we could never in "classical" terms discern the events in the earliest microseconds of the creation event.
Now M-Theory does seem in some respects to transcend this difficulty. But the energies necessary to test it are thus far, are likely forever unobtainable to us. But it's such an aesthetically beautiful theory, that entire careers in physics are devoted to it.
I think this is essentially the view, though I'd welcome any comments or clarifications.
Best to You and Yours.
Glory to God.