Awesome. I now see that the app's Play store listing explains this:
When started, Electric Sign will download and display a user-specified web page, then go to sleep for a specified number of (minutes/hours/days). It will then wake up, re-download and refresh the web page, and go back to sleep again.
The eInk screen is low power to change, and requires zero power to stay on.
The device sleeps between screen refreshes, and the WiFi power use in minimal.
My nook art screen lasts over a week with refreshes over the day. I don't know of a tablet which has a screen-on time for that long.
https://shkspr.mobi/blog/2021/09/turning-an-eink-screen-into...