One can simply look at the right-hand-side of their browser window and see the scrollbar height to gauge "accurately enough" whether it's long or short.

More to the point, I would expect anything purporting to be an "ultimate" guide to ffmpeg to be a massive time sink that simply can't (and shouldn't) be ingested in one sitting. It's either going to be incredibly dense or it's going to leave out innumerable details, leaving many things implicit. Don't get me wrong, there is nothing wrong with those approaches, but it means that "how long" it takes to read will depend on the reader and what they actually end up reading.

   if (mins < 4) return "a couple of minutes"
   if (mins < 8) return "five minutes"
   if (mins < 12) return "ten minutes"
   if (mins < 18) return "quarter of an hour"
   if (mins < 25) return "20 minutes"
   if (mins < 40) return "half an hour"
   if (mins < 50) return "45 minutes"
   if (mins < 70) return "about an hour"
   if (mins < 100) return "hour and a half"
   if (mins < 250) return "a couple of hours"

Also, is the "couple of hours" estimate being off by more than a factor of 2 a typo, or are you just trolling at that point?

I wonder if that is a purposely value, trying to use the same psychology as Supermarkt prices, where they say "0.99" rather than ""1.00"?

In my opinion the right approach however is to have a clean layout, where my scrollbars gives me a good estimate on the length, so I can make my estimate based on my reading speed and experience. But yeah, ads and other stuff make that of course impossible.

And it's definitely better than "number of words" or "A4 pages", since I have no idea how fast average person reads.