Chapters seem to be correct. Checked it with Sigil.
I've reset the Time To Read. It quickly stabilized, indicating a speed of around 37 paged per hour. The measured time was accurate. After checking the three books above again, times were all over the place; it now indicated 4h for the first book, and around 40 and 13 for the second and third.
Maybe the kindle needs some time to stabilize with each book.