I'd say that if Plato's account is so garbled that he gets the date off by thousands of years, the entire story is likely to be useless as a source of actual history.
Is is possible that for an ancient Greek to describe an event as "ten thousand years ago", he means nothing more or less than "too long ago to remember when, exactly"? It may be unfair for us to backport our modern conception of numbers as these very precise values.