Once you melt the chocolate in the microwave or double boiler, it will stay warm for about 30 minutes prior to pouring it into the fountain. All domestic fountains have a heat element to keep the chocolate melted.
If you need to have the chocolate melted more than 30 minutes prior to using, place the chocolate in a fridge bag, wine bag or a polystyrene box to contain the heat. This should keep the chocolate melted longer.
If you are using a bowl to serve the chocolate, please use a microwaveable bowl. This way you can melt the chocolate once it starts to harden. Liquid Chocolate is PURE Belgian chocolate, so it will go hard as time goes. How fast will depend on the temperature in the room, on average 20 - 30 minutes for it to go hard.