very stricly enforced at least in my experience.

kisoks is programmed to disallow. in MDW this summer supervisor wouldn't accept my one bag destined for CLE 4hr 30min before flight. This is despite A+ status and us all being on business select fares. Wanted to take the train to downtown to visit the zoo without lugging my bag around.

I said I guess I need to have you change my flight to the earlier one, check my bag, and then immediately change to the later flight. She agreed that would work, however my flight was oversold so she couldn't protect my seats if cancelled.