I made cupcakes with Betty Crocker frosting. Do they have to be refrigerated if not serving until the next day?

That is a great question!  Your cupcakes will not need to be frosted if you are serving them the next day.  Our general rule of thumb is:  if you are using them within 2 days, store cakes and cupcakes loosely covered, outside the refrigerator.  If using from 2 to 7 days, store them in the refrigerator, tightly covered.  I wish I could be there to sample them for you!