Maybe I could use my dog instead of NTP and have her press a button that syncs my computers to exactly 20:00? Would work offline at least.
Not sure if he’s relying on other sensory information like certain smells or sounds. I don’t believe that’s the case; we didn’t replace the broken feeder for 3-4 months and he was able to keep time within a few minutes during that period. Our behavior is erratic and changes often; we work jobs with very inconsistent schedules (thus the automatic feeder) so it’s likely not that our behavior is prompting him as well. We can even observe him consistently going to his feeding area on the security camera at the correct time when no one is home. Interesting stuff!
And to further make it weird: our vet told us to feed him multiple small feedings throughout the day so the feeder was programmed for 6 feedings with 2 hour intervals from 9am to 9pm. He hit the mark for all feeding times!
I still think there is potentially some sort of external prompt(s) though. Circadian rhythm is an excellent idea. Maybe that combined with something hard to detect, like lighting levels (which would explain why the timing shifted a few minutes over a few months). Who knows!
At school we used to have a bell mark class ends and without a clock or a watch I could predictably tell when the bell would fire. One time I demonstrated this to a friend (both of us kicked out of class) by counting down from 10 on the second to when the bell rang while looking at a blank wall.
Strange. But nonetheless true.
...or add it to systemd (it will get there eventually anyway)
[1] https://en.wikipedia.org/wiki/Biff_(Unix)#Origin_and_name