Here's my laundry rule that @aaiyar was thinking about:
Or in text in case anyone finds that more helpful (screenshot in the link above):
Trigger events: Power level of Washing Machine Plug reports >= 30.0
Actions to run:
Wait for event: Power level of Washing Machine Plug <= 20.0
Wait for event: --> elapsed time: 0:01:00
Speak on TTS device: "The washing machine is done!"
Notify notification device: "The washing machine is done!"
You may need to adjust the power levels and the wait time to match what your washing machine actually does or how your smart plug reports, but that's the general idea (and what works for my particular case).