Step 10: Demold
Now, you wait. The plaster should cure in thirty minutes or so, depending on how thin you mixed it. It will heat up noticably while curing. There is actually a chemical reaction going on that solidifies it, it's not just drying out. Once you can see it's no longer liquid, touch the back periodically to feel the temperature. When it's gotten warm and then cooled down to room temperature again, it's safe to take it out of the mold.
Pretty freaky, huh?