Definitely at least a few weeks, largely because of how everyone has affairs to put in order, assuming it's Sora retaking the mark of mastery exam. In fact, Sora says that he has some things to take care of. Even by the time that the secret ending rolls on, Goofy laments to Donald that Sora's late. Yep, it's definitely going to be over a week, whatever Sora's doing at the end of the game.