Is there a way I can speed up the drying process? I've got a fan in front of them but it's still very slow to dry.
Actually, you WANT heat to help it dry faster. Try putting it under a desk lamp or place in the oven with just the light on.
How slow is slow? Is it possible it came in contact with grease while mixing? How thin is the icing? How thick is the piece?
Heat should help them dry faster. Is it really humid where you are? Maybe humidity is the issue.