There are a few pieces of knowledge about molding and setting chocolate in the molds that deserve attention. I have searched for answers and found some at http://www.candylandcrafts.com/chocolatecandymolding.htm
My basic interpretation of them are:
1. Chocolate needs to be heated to between 98 degrees F and 100 degrees.
2. For larger molds, the best results for setting the chocolate are about 10 minutes in a freezer.
Peach has indicated that the demolding step is accomplished by allowing ice in the middle to melt, so this implies time for super-cooled water to freeze, which may not happen in that 10 minutes.
I don't have a good idea on how long it will take for that ice to melt.