Usually, dry ice will last from 18 to 24 hours in a cooler. They can last as little as 3 to 5 hours when in the outdoors, though so keep that in mind. You'll want to have other ice or alternatives mixed in to increase longevity. Dry ice is colder than regular ice so it should be able to keep your cooler colder for longer. If properly taken care of and put in a large enough cooler, dry ice could even last a few days.