The prep time does not include the time for the chocolate to harden.
The cook time is approximate. Depending on your microwave, it may take a little less or a little more time to melt the chocolate. Only microwave the chocolate until it is barely melted. Do NOT overcook it or it will not spread and will lose its shine.
If you don't have a microwave or prefer to use the cook top, melt the chocolate using a double boiler. Place an inch or two of water in a pot. Place the pot over a burner and heat the water over medium heat. Place 8 to 9 ounces of the chocolate in a bowl that will sit partway inside the pot. (The top of the bowl needs to be a little wider than the pot so the bowl will not fall into the water. The bowl should sit just above the water in the pot.) With the bowl of chocolate placed in the top of the pot, stir the chocolate until it is melted. Do not let any of the water get into the chocolate. When the chocolate is melted, remove the bowl of chocolate from the pot. Add the remainder of the chocolate to the bowl and stir until it is melted. Then follow the remaining instructions for the microwave method.