The starter should be left at room temperature. Drape loosely with dish towel or plastic wrap. Do not use metal utensils or bowls. If using a sealed Ziploc bag, be sure to let the air out if the bag gets too puffy.
Your yield may exceed 4 cups depending on the temperature of your kitchen and eagerness of your starter. If this happens, reserve one cup for baking and divide the remaining batter into Ziploc baggies of 1 cup each to freeze or share with friends.