George's original conception was that the evil Empire was more or less timeless, and the whole Star Wars universe was based on the for-all-intents eternal struggle of the forces of good against the Empire.

I don't think there is anything in Star Wars, ESB or even ROTJ that necessarily contradicts this. Ben's yearning reference to a time "before the dark time, before the Empire" could be a reference to something extremely ancient and remote. There's no reason it wasn't 200 or even a thousand years before the events of SW, and Ben was the last of a long dwindlage of torch-bearers.