PlayStation Universe reports that Famitsu magazine reports that the PS3-exclusive Final Fantasy XIII demo will clock in at more than two hours, which is longer than the CGI movie bundled with it, Final Fantasy VII: Advent Children Complete. The bundle releases March 2009.
The demo will be on a separate disc (ah ha! Blu-Ray has its limitations too ya know!!!!) The demo will be based on the opening to the game, naturally. Wouldn't be smart to spoilerize everything. Two other tidbits, I'll fess up and say I have no clue what these mean so I'll just quote verbatim: "One of the female characters, refered to as 'Pigtails Girl', has been through some tough times". And "Mr. 33CM's real name is based off of weather as well".
Final Fantasy XIII Demo to Last Over 2 Hours [PlayStation Universe]