Would anyone happen to know if (and when) Seconds was ever on network television? And where can I find info about that if it exists online?

I know I saw it on TV back in the early 1970s, but I believe it was on a local broadcast channel, but I can't imagine it not premiering on one of the three networks' "Saturday Night..." or "Sunday Night at the Movies"-type time slots. You might want to identify network movie time slots from the late '60s and early '70s and see if you can find lists of which movies aired. Just as a test, I googled NBC Saturday Night at the Movies and found a few lists, but none from the period when SECONDS would have aired. But then, I find Google results lately, no matter what I search, to be wildly inadequate.

Maybe someone on the TV board at Home Theater Forum might know.

I first ran into "Seconds" on local television in the very early '70s. At that time the local station had this brainstorm (maybe it came down from a "consultant") to clip the credit sequence off the front of the movie and run it after the movie was over (there weren't really long final credits on movies in those days). In this case, though, they actually jumped from the ending perhaps 30 seconds to a minute early and went to the 5PM local news. I was outraged as only an adolescent can be outraged and called the local station, complaining that they cut off the ending to the film. I won't give a "spoiler" , but let's say it's an unusual and very dark ending. The person answering my call said (without taking the time to check, of course) "That's the movie they sent us; it must have been a 'Hitchcock' ending." Because this was in the days before video, it was several years before I could see the film with the complete ending.

Given that it is black/white, and came at the latter days of big studio films produced in black/white, I'm betting it never made the prime time movie slot.
It wasn't a hit either. In Cold Blood, I believe the last Hollywood produced black/white film, got network prime time in early seventies, but it was a hit movie and network made a big deal over it.
CBS used to have a late movie that aired against Carson. A big chunk of these were sci-fi/horror. I'd start by trying to find out what aired on the CBS Late Movie.
Whatever info you do find probably won't be official. It'll be some guy's personal project to put together a list of movies that aired on a particular network movie slot.
Best bet is find tv listings from first few years after movie's release.