2520 years from 539, when Babylon fell the first time, is 1981. But if you add the 15 years Hezekiah added to the calendar, it comes up to 1996. This is exactly the end of the six days from Adam (6K years from 404 BC).
This also happens to be when things started changing rapidly. The White Squall movie Q points to as our beginning, for instance, came out at this time.