If you do Easy, Medium, AND Hard all in a row, it lasts more than 24 hours. Actually, it lasts more than 32 hours if you play all three difficulties.
It lasts less than 3 hours, 4 minutes. Some dude played it while watching Kung Fu Panda twice and finished the campaign before the credits rolled second time around.
...well, it was his second time through. His first save got deleted so yeah, he was probably running it faster than usual.
Was it? Fair enough, I failed. Disregard everything! I got the two games mixed up because I don't care about either of them