I read mostly just in bed before going to sleep, averaging around 30 minutes. The Count of Monte Cristo took me three to four weeks (I don't keep notes on that, so it's an estimate), and I'm not a speed-reader. It's just a book that has aged well (i.e., a limited cognitive overhead) and is not particularly hard to read in the English translation.
On the other hand, it lists The Canterbury Tales for 64 days, which seems reasonable given that reading English that old really does take a lot more effort (and that's assuming an annotated edition), but way out of whack compared to Dumas' novel above. (Also The Canterbury Tales is not a work I read in one go; a couple of stories before moving to another book is sensible here in my opinion.)