Presumably, those 15 hours would have been spent continuing to monitor the situation, evaluating options, and seeking creative solutions. Since we know the key factor was the fire situation around column 79, if the building had lasted longer it would have been because the fire hadn't got there yet, or because it passed before the girder had completely walked off.
After the 1993, bombing, for example, there was great urgency about bracing the columns laterally (and even leaving debris in place that was doing this until braces could be put in place).