I would not set my clock back to March 20 if I reset my island, which I have no plans of doing. I started over a lot in new leaf and I never set it back to the original start date. I personally prefer it to show how much time I actually spent on that island or town instead of just the original release date of the game, even if that was when I started playing! I also really don't want to time travel on my island, because once I start, I don't think I'd be able to stop from doing that whenever I wanted.