I understand, but there are two things at play here:
1. I don't know where the Kindle gets the page numbers for non-Amazon books. These are converted EPUBs. If I remember correctly, Calibre has an estimation function for pages; so maybe Calibre puts them in.
2. I have read all three books as hardbacks. There is NO way I would need almost 40 hours for the first (much less), and NO way I needed only 15 hours for the third. These books are all in the same ballpark with regard to reading time. I know from experience.