Imagine a ship made of 365 planks. (Or, since sometimes people are initially inclined to try to lawyer their way out of dealing with the hard problem...

Imagine a ship made of 365 planks. (Or, since sometimes people are initially inclined to try to lawyer their way out of dealing with the hard problem here by talking about the nails, masts, etc., we can just say 365 *parts*.) Every day, someone swims out to the ship, takes off one plank/part, and replaces it. At the end of the first day, there are 364 original planks and one new one, at the end of the first week there are 358 original planks and seven new ones, and at the end of the year there are 365 new planks.

If the ship made of old planks at the beginning of the year is a different ship from the ship made of new planks at the end of the year, when did the old ship stop existing....exactly?