Once you stone has hardened you are ready to remove it from the mold. Different formulas of cement take different times to harden. If you use a quick dry cement or an accelerator it will harden quicker. You will be able to test the hardness using your fingernail. If it feels like stone it is ready. I normally let mine sit overnight. In the video below a week is recommended. The main thing is to not remove it from the mold until it is completely hard. If you do it will fall apart.
To remove the stone from the mold just lay down a towel and flip the mold over onto the towel. Pull on the edges of the mold gently all the way around and push gently on the back of the mold until you feel the stone release. It should fall onto the towel. Once you have the stone out you will remove the contact paper and scrub any cement off the top of the glass and then put the stone on some dowels or a rack so that it can fully cure. This may take a week or so.
The widget below features diamondcrete, stained glass patterns, molds and a nice program for resizing patterns called rapid resizer.