How long until you can see your town history?
How long does your town tree have to grow until you can sit on it and see your town's history?
I think this can help. I didn't know of the town history feature, but my guess would be that you'll unlock it as soon as you get it to the "fully grown" status, which means 500 hours + 500 days.
Based on the other answer and the fact that I was able to see my town's history as of yesterday (I got the game on release date, which was about 50 days ago), I'd say 50 days and 50 hours.
