The timeline was obviously not a planned aspect of the story originally and I personally don't find it particularly great storytelling but there is evidence in interviews of a timeline document existing internally since at least 2002[1] (where Shigeru Miyamoto explicitly said they do take it into consideration when writing the game's story but primarily focus on the games individually).

Maybe they did release the timeline because of fan pressure but some sort of timeline did exist for at least a decade before they released it which doesn't fit your theory they just came up with something and released it in secondary media because of fan pressure.

[1]: https://www.nintendoforums.com/articles/40/super-play-magazi...