I made a timely video.
https://youtu.be/PnJZSk4JHFM
Timer switches: literally just a clock and a switch

YouTube

@TechConnectify
Reminds me that there was a mechanical, rotary time switch mounted on a wall in my old flat - in my years of living there, I never did figure out what it was attached to...

(Place was built in ~2008. I'm now wondering if it's a common US thing - it was next to a massive GE washer-drier thingy.)