We don’t recommend it. Slow dispensing seems to be a common criticism across most brands and models. Since cooling the liquids usually slows their pouring, refrigerating batter overnight could actually lengthen your cooking time, especially if the batter gets stuck in the spout. If time is a major concern, mix your dry ingredients ahead of time and leave them in a sealed container on the counter. Then add your liquids in the morning, so at least the dry ingredients and your container will be at room temperature.