I have never made a gumpaste shoe so not much help there. But, I know gumpaste dries pretty quick. I make gumpaste flowers and they are dry overnight. If you make the shoe on Thursday I think it will be dry by Saturday. I am sure someone with more experience will have better advice. Good luck!
Unless it's incredibly humid, you should not have much problem.
A couple of tips - roll out your paste as fine as is practical, and for the heel, if it reasonably thick, poke a hole through from top to bottom with a skewer, so that the air can circulate. Dry all the pieces on foam, again so the air can circulate.
If humidity is a problem, dry under a desk lamp.
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