Album Rock stations did it first, I think. Double-shots, two in a row by each artist played all day on Tuesday. Two-For Tuesdays the first guy called it. Catchy name and it was a big success, a programming idea that was soon widely used in lots of formats.
Non-music units may have start and end dates and also start and end times. This can minimize the need to move promos (for example) into and out of the category during the campaign run.
