Vonnegut is ultimately pushing back against the old saw of the captivating first sentence, many aspiring writers fall into the trap of trying start their book by trying to captivate the reader at cost of laying that foundation; if I can just word this opening paragraph perfectly, the readers will be hooked. It is a fairly dishonest way to go about things. Everything the reader needs to know about what you are writing needs to be covered in that first chapter or paragraph or chapters or section or whatever metric applies to what you are writing, the trick is that you need to present it in a way that does not spoil everything to come.
If you get fixated on captivating the reader with the opening, tossing the first chapter and reworking the second is decent advice, but it might be better to just rework the first. All of these pithy bits of writing advice have truth in them and have a great deal to teach you but far too many aspiring writers tend to accept them as dogma.
I think there's something effective about the way the book begins, and continually references other parts of itself throughout the entirety of the story; but it's definitely not throwing away the first chapter; or alternatively if there was a "first chapter" to Slaughterhouse-Five that Vonnegut threw away, I wonder what possibly could have been there.
Why would "A blue Ford just parked in front of the door. Jim still hasn't truly fully woken up but he was already making breakfast..." incite me to read the book?
Compare that to The Poppy War which I just discovered:
"Take your clothes off. Rin blinked. What? Cheating prevention protocol."