Of course stations could "start signing off at midnight" to save $$$$. They could sign off it 7 if they wanted to. Or 9. Or 10:47. As long as they are on at least half the time of their license.
And popularity has nothing at all to do with "saving money." Only 20% of the daytime listening audience is available to listen to all night radio ... 1/5th the population. Are many stations going to "save $$$" for that? Not a lot, so, they keep it on "just in case" of an emergency situation ... not because of the perceived popularity of George Noory. Only 20 percent of the audience is available.
Now, with today's "energy efficient" small wattage (1000 watt or so) transmitters, the portion saved on the power bill for four or five hours of downtime is neglible ... like, $50-$100 a month or so. If that. (I know, I've paid such a bill for years.) Keeping a few lights on, a board, a sat receiver, a couple of computers ... neglible.
Most stations don't make money all night ... or at night at all. What you hear are "trade outs," "bonus spots" or other things to "fill the gaps." Few stations, outside of infomercials, get local direct money for being on "all night." Also, keep in mind, that AM radio, alone, only serves on a good day 20% of the available audience, with 80% going to FM. Now, a station like 'PRO with a greater majority of that 20% audience does quite well. But a station with a 1.5 share ... well, not so meaningful.
It's a convenience to "stay on" all night and a "reassurance." Not a money maker. But could they sign off? Sure. But to save money? Probably not a major consideration with the state of automation and remote control capability available.
Now, as to Holland's post ... he's right. July 28th at 1:00 a.m. ... just hope that stations stay on that long. It's the end as we know it. Surprised you guys didn't hear about it. I'm four time zones away and I got hint of it already.
That's why Holland's a great consultant. He's on top of it. But after tomorrow ... you all night board ops, be on the lookout. That troposcopic ducting from 540 to 1710 will be a doozy. I'm sure Noory will have details tonight on Coast to Coast ... for those who run it and not sign off.