It matters not "what they realized" - if the US President asks for air time, the US Networks are going to give air time. Anyone who watched the US evening news should have anticiapted networks broadcasts delays at 9PM.
der Brucer
A few of them, yes. On the West Coast, we don't often get impacted by such events. Many times, the speeches are over by the time we get home from the evening commutes.
Locally, Fox, NBC, CBS, ABC and one PBS station will air live coverage of such a speech. Fortunately for me (and many more like me), the rest of the ComCast programming airs unscathed.
Sometimes, the major networks air the programming being preempted on alternate local stations.