its actually the 255th day since the first day is the 0th day.
If you say that the 1st day is the 0th day, then why do you call it the 1st day?
And, reasoning further, this implies that the 2nd day is actually the 1st day, but you already defined that as the 0th day, so the 2nd day is the 0th day as well. And the 3rd, and...
Perhaps next year celebrate with ... Pi?
No that's on Pi-day (March 14th)
Also, what do we learn from all these celebrations? That geeks are taking over the world.