The Wikipedia page for Jules Vernes novel Around the World in Eighty Days comments that Verne is often characterised as a futurist or science fiction author, but there is not a glimmer of science-fiction in this, his most popular work.
Well, there is no generally agreed-upon definition of science fiction (see this list of proposed definitions; my own view is that its a family-resemblance concept for which no precise definition should be expected). Some definitions do require that the storys milieu be different from our own as the result of scientific or technological advances and by that standard Around the World indeed does not count as science fiction. But at least one popular definition or family of definitions focuses merely on the idea of a story that depends crucially on some point of science without necessarily involving extrapolation to some alternative milieu. Given that the plot of Around the World turns on the fact that one gains or loses a day when crossing the international date line, the novel thus does count as science fiction by some definitions (geography being, yknow, a science), so the not a glimmer line is something of an exaggeration perhaps yet another example (see here and here) of the bizarre resistance on the part of some Verne fans to seeing Verne characterised as a science fiction writer. At any rate, those who make these pronouncements seem oddly incurious about what the proper contours of the concept of science fiction might be.
I would add that Vernes Captain Hatteras, generally not considered sf, has even greater claim than Around the World to the category, since it portrays a successful expedition to the North Pole at a time when this had not yet happened, and speculates (inaccurately, but not impossibly) as to what would be found there thereby turning (unlike Around the World) not just on a point of science but on an extrapolated future development of a science (viz. geography); and similar remarks apply to Five Weeks in a Balloon and Measuring a Meridian. Those who deny it the title of sf are implicitly assuming, I suspect, that the only relevant extrapolations of science are those that involve new technology.
I loved maps as a child, so I was very young when I found out what the international date line was. I was a pretty literal minded-child, so when I learned that you “gained” or “lost” a day when you crossed the line I thought you literally moved in time , and that if you repeatedly circled the globe traveling east and completed each circumnavigation in less than 24 hours you would travel into the past. I was terribly disappointed when I found out it didn’t actually work that way.
This reminds me of a thought I had about what the first serious sci-fi movie was. I thought it was Forbidden Planet in 1956, but then The Day The Earth Stood Still from 1951 came to mind (Metropolis might also count). But is the latter sci-fi? It has a space ship and two aliens, but takes place in then-contemporary times. That’s certainly not the case for Forbidden Planet.
Star Wars and Battlestar Galactica can’t be sf either, since they both take place in the past.
Verne is good, but was he sound on Plotinus?
I don’t know. He was sound on many things and unsound on many things. (For example: he sympathised with blacks and native americans but was rabidly anti-semitic. Which just goes to show, it’s always something.)
Authors who were against some form of racism/prejudice but in favor of others are actually pretty common, for instance Mark Twain had some pretty nasty views on native Americans, or these two sets of WWII-era cartoons from Dr. Seuss (let’s put it this way: one is consistent with The Sneetches and the other isn’t, and let’s not even get into his pro-FDR, anti-isolationist views):
Don’t you mean SyFy?
Don’t you mean ΨΦ?
The gaining-a-day plot point was taken from Edgar Allan Poe’s story “Three Sundays in a Week”; Poe’s role in the development in science fiction is even more neglected than Verne. Coincidentally the page of definitions you link to includes Hugo Gernsback’s one as “the Jules Verne, H. G. Wells and Edgar Allan Poe type of story”, as that quote indicates he considered Poe to be the equal of Verne and Wells, all three of which were frequently reprinted in Gernsback’s magazines.
Verne also wrote a long essay or short book about Poe, titled “Edgard [sic] Poe and His Works,” and his novel The Sphinx of the Ice is a direct sequel to Poe’s Narrative of Arthur Gordon Pym — as, in its way, is At the Mountains of Madness by Lovecraft (whose essay “Supernatural Horror in Literature” also deals with Poe).