I think it was Robin Williams that said time is nature's way of keeping everything from happening all at once. So, based on that, #2 is ruled out.
I'm going with #1, time is serial. Until, there is proof otherwise, I can't see any other answer. Every historical artifact that has been uncovered proves civilization has advanced over time through carbon dating, etc. Nothing has been found from the future to support a fluid existence of time. Until there is proof otherwise, serial is the only answer. The rest are just theories.