To them, a couple thousand years passing probably just feels like a year or two passing for us.
In any case, while Feige didn’t confirm that The Eternals will indeed stretch over tens of thousands of years like in the comics, his comment to Collider indicates it’s on the proverbial table.
This is one of the superhero properties that it’s possible to take such a creative approach with, as the Eternals, while not full-on gods and immortal, are incredibly powerful and have lived for millions of years.
We’ve seen flashbacks in previous Marvel movies that have been thousands of years before the present day narrative, but the prospect of having The Eternals’ main story stretching over tens of thousands of years is intriguing.