According to Self-Publishing School [1]https://self-publishingschool.com/how-many-words-in-a-novel/, on average, there are about 300 words per page in a book, so 100 pages means 30,000 words.
According to Mindtools.com [2]https://www.mindtools.com/speedrd.html, Most people read at an average rate of 250 words per minute (wpm), though some are naturally quicker than others.
So if you divide the 30,000 (words) by 250 (wpm), you get 120 minutes which is 2 hours exactly.