Well, I would say a variable length of something between 10 hours to 50 hours.
Basically that means if you want to rush thru the game during the replay doing only the key quest that progress the story, you can rush thru it in 10 hours. But if you were to do all the side quests, play a bit of cards and what not and take yoru time, it would take 40-50 hours to complete, excluding things like deliberate long hours at the pazaak bar.
Also, I would love to see pazaak accessable outside of the loaded game. Basically we should be able to just play the cards without logging into the story... its better than playing Hearts by lots.