I've had my non-Evo MK25 to 34f for 42 minutes. I was told by a local ice dive instructor for ERDI that most icing occurs because the diver was breathing heavy on the regulator prior to entering the water. He recommends a test purge during buddy check, wait 5 minutes, then enter the water and place regulator in as you are submerging. He swears by this method and swears it works. Note* sub 40 is cold, unless it is something really interesting it keeps even the strong willed on shore.