Small body mass. I wouldn't leave them at room temp for hours, they'll grow bacteria. I just drop a frozen one one in a largeish Tupperware with at least 2-3 cups of warm water (around 110 degrees) and put the lid in. Maybe for 20-25 minutes or so. Hit it with a hairdryer or dunk it in fresh hot water for a minutes if I'm feeding something heat-sensitive.