Christmas Eve may be slightly busier than the usual travel days. If your connecting IAH-CUN is oversold and your MSP-IAH delayed, the GA may be very eager to process stand-by passengers at T-15 minutes. The subsequent IAH-CUN flight could be full.

This could be one of the times where you might benefit from the longer connection time, but if potential one-day delay doesn't bother you (no prepaid hotel, etc), then you can stick with the shorter connection time.