Twelve cases for Sherlock Holmes, and they are twelve separate short stories — nothing carries over, eighteen to twenty-five minutes each, and you can read one and stop. A king is threatened with a photograph. A pawnbroker is paid four pounds a week to copy the encyclopaedia out by hand. A woman's sister walks out of a bedroom locked and shuttered from the inside and dies in the corridor. At Baker Street, Holmes reads a shiny cuff or seven splashes of mud on a sleeve before the client has finished sitting down; Watson writes it up afterwards, once fetched from his own breakfast table by telegram. The shape repeats — a stranger talks, Holmes names the answer, the reasoning arrives last. Read straight through, you will feel the joins.
The Adventures of Sherlock Holmes is 104,539 words. At an average adult reading pace of 300 words a minute that is about 5 hr 48 min, or roughly 4 hr 21 min if you read quickly and 8 hr 43 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.