Final Fantasy games are not short. So while big titles from other developers might be clocking in at somewhere between 7 and 9 hours, don't expect a short Final Fantasy XIII experience. Expect a long haul.
In a recent interview (pictured below), FFXIII director Motomu Toriyama noted, "For XIII, the size of the entire game is considerable. Just running through the main story takes experienced players over 50 hours. For the first time, I think it's possible to play through in full in about 60 hours or so."
Meaty! Players have been waiting three years for this game, and it sounds like they've got a big game ahead of them to experience.