I usually let my cakes thaw overnight to be sure they've come completely to room temperature and won't give off any more condensation. If you don't have overnight, give it at least 3 hours and then test it. If you're doing an edible image you don't want to risk little beads of sweat popping up on it!
Good luck!
I take my cakes right out of the freezer and decorate them without defrosting and I never had a problem with condensation. I have never used edible images. I think the icing seals in the moisture and it just makes the cake that much moister.
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I am using 1/2 butter & 1/2 crisco icing and will be putting an edible image on the cake (12 square). How long does it need to thaw.