People that have the radio on at work
-Some Military MOSs
-Anyone driving all day (Truckers, Emergency Personnel, Postal Workers, Realtors, etc.)
-Anyone with the radio while they get to work
...to name a few. I'd imagine the 7pm radio crowd might be smaller.
Me and my 2 hour commute (northern Virginia FTL) checking in.
And you're right, radio is pretty much the opposite of tv in terms of what is considered "primetime." In radio, primetime is the morning show. That's where all the listeners are