The Day Out of Time marks the end of one solar cycle and the next.
The Day out of Time, which falls on July 25 each cycle, is the day before the new year.
The new year begins with July 26th and ends with July 24, only 364 days. The missing day is The Day Out of Time, giving the calendar 365 days.

This topic and others such as Day out Of Time is explained here, and perhaps you'll understand why it is celebrated.

Kin 68
Yellow Electric Star
I Activate in order to Beautify
Bonding Art
I seal the store of Elegance
With the Electric tone of Service
I am guided by the power of free will
Castle 2: White Northern Castle of Crossing
Wavespell White Worldbridger

Waning Crescent
Waning Crescent