No matter how far you go back in time, it'll always count as one new day. Like if you go to 02/19/15 it will count that as 'tomorrow' aka the next day.
- - - Post Merge - - -
The only con to tt'ing backwards is trying to get back to 'today', because fowards every day counts.
Unless someone decided to move out in a few days, then you can tt forward as far as you like without losing a villager.