As part of the rule set up, one of the values you enter is the maximum shift time. This prevents supervisors from over-scheduling employees. If you need to make this change, go to

MANAGE MY BUSINESS->MANAGE DEPARTMENTS and edit the department in question.

NOTE, if you receive the message you need to go to MANAGE MY BUSINESS, MANAGE SHIFTS and define how to handle larger shifts. This message tells you that the rules for shifts larger than 13 hours have not been defined.