Well as we all know any form of magic only has a due time limit of how long it last, and since most of the norts and possibly others are from a different time line, they probably couldnt be out of there or own time for an estimate of I guess more then half a day maybe or less, thus them having to go back to they're own place. But if we think about when he said "light and dark being short" It could mean that he simply is waiting out for Team Nort to have it's thirteenth member and the Keybladers team to have it's seventh member so that he may complete the X-Blade when it is time.