I'd think that a simple explanation that MCT is established for a reason would suffice. I wonder if down the line UA will catch it and change the itinerary. When the connecting time isn't met, the computer (all of the systems) flag the PNR very clearly, telling you which segments don't work. You CAN force the record to end, but it's not wise to do so. If a travel agent forces a connection and something happens, it will come back to the agency. When UA breaks their own rules, they have only themselves to blame. And they even told the customer they were breaking their own rules! I hope the conversation was being recorded for "quality assurance."