I am flying in Tuesday through Friday so game time doesn't affect me, I just prefer night games for sake of national exposure.
I think the best national exposure during the last 2-3 innings of a great game. SOme of those 4:30pm starts get great national exposure during a great finish as people are getting ready to turn on the late game. If they aren't dedicated to one of the teams, they have shut the game off by 11:30pm (or if they are huge mlb fan in general) and miss the drama anyway.