Dr. Mortimer, a country doctor from the Devon moor, brings Holmes a family manuscript dated 1742 and a fresh death. Sir Charles Baskerville lay in the yew alley of his own grounds, where he walked every night; twenty yards off, unremarked at the inquest, were the tracks of a very large dog. Sir Henry, the heir, has just come over from Canada to take the house. Holmes pleads a blackmail case in London and sends Watson to Devon in his place, and be warned: for about a third of the book Holmes is off the page and Watson is alone on the moor, filing reports home. The dread works anyway.
The Hound of the Baskervilles is 59,174 words. At an average adult reading pace of 300 words a minute that is about 3 hr 17 min, or roughly 2 hr 28 min if you read quickly and 4 hr 56 min at a more deliberate 200 words a minute.
That count is measured from the complete public-domain text rather than estimated from a page count, so you can compare all the books side by side.