Sourdough starter is not as efficient as instant or active dry yeast at leavening. Ingredients such as eggs, milk and cream slow fermentation down even further so you’ll need to give your batter at least 8-hours to rise. Your batter should look bubbly when you’re ready to make your waffles.  You can make the batter up to 16 hours in advance, any longer and it they may develop an unpleasant sour flavor.