I don't think it's a joke, it's a correction of attribution. The quote seems to have been attributed to a lot of people, but earliest mention of similar message is indeed from Blaise Pascal, see https://quoteinvestigator.com/2012/04/28/shorter-letter/
Quote Investigator is a gem. There's another page[1] on a similar quote:
> If it is a ten-minute speech it takes me all of two weeks to prepare it; if it is a half-hour speech it takes me a week; if I can talk as long as I want to it requires no preparation at all. I am ready now.
~ Woodrow Wilson, as quoted in The Operative Miller 23
> If it is a ten-minute speech it takes me all of two weeks to prepare it; if it is a half-hour speech it takes me a week; if I can talk as long as I want to it requires no preparation at all. I am ready now.
~ Woodrow Wilson, as quoted in The Operative Miller 23
[1]: https://quoteinvestigator.com/2014/03/01/short-speech/