Well, we know the footprints were left between 20:01 UTC on April 24 and 16:01 on April 25.
I recall sunny days where if felt like it should be warm, but it was still cooold. But ice certainly sublimates in such conditions. Wet clothes on the clothesline would freeze-dry all the time. A 4' tall snowman that got only morning sun, over the course of a cold January, got skinny and leaned over and nearly touched its head to the ground. (It had a few inches to go before it tumbled over).