That could be an important variable, choosybeggar. If a thick layer of ice forms on it, it will definitely slow the heat xfer rate.
And the more I think of it, even though the freezer is obviously colder than the room, relative to the dry ice it is hot air. If the fan is circulating and the dry ice isn’t covered, the “wind” of the freezer might actually sublimate the dry ice more quickly than a block on the counter, especially one with a coat of (real) ice.
I think it’s time to experiment!
The (water based) ice will slow down the sublimation. If you try dry ice in a 2-liter bottle with water in it, the pressure shoots up very quickly, but then slows down as the dry ice gets a layer of ice on it.
End result is the same - a surprisingly percussive explosion.
Anthracite- I’ve seen a few CO2 2-liters go off. The first one I saw actually broke into lots of pieces, none bigger than 1 square inch. It was very cold outside that night, and that may have had something to do with it. The others seem to rip in half, usually through the thick part at the top, all the way down the sides, with the pieces held together with the bottom.
A college friend had one go off in his hand. It had baking soda and vinegar in it, so I don’t think it had quite the wollop (because the vinegar displaced what would have been high pressure CO2). His hand was quite swolen. And it went off indoors. I’ve never heard anything as loud as a 2-liter bottle expoding in a non-carpeted brick stairwell.