Wow! It's joke!
To avoid conflicting with the too-close holidays of Fan-Ball's Anniversary (April 2nd) and GhostCheese's birthday (also April 2nd), Japes Day was proposed to take place on February 25th. It would function entirely as April Fool's Day had in the past.
The holiday was proposed, with the hopes that it would garner attention and be put to good use the following year.
The story Playground: The Dark of Pluto was uploaded a day later than intended due to site complications.