Going by how they threw a giant city sized dice in previous chaps, and looking at the raws I am getting the sense that this is Pageratta's version of a South Park type story where anything goes.
These are all real holidays, not jokes/puns made up for the manga (at least as far as I could gather)
It's just that many Japanese holidays are placed based on the numbers of the dates.
So for example the numbers 1 and 5 can be read as Igo, hence why they made January 5th Go day.