First, I should say that I have a similar automation set up using Rule Machine. In my case, here is my setup:
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
Notify notification device: "The washing machine is done!"
(You will likely need to adjust the wattage and time values to match the behavior of your machine; this works for me.) That being said, it seems like this should be do-able in Basic Rule too, aside from the fact that my rule waits until the power level is high to kick things off instead of just waiting for it to remain low. You can add that to Basic Rule, but it's a bit awkward since it forces you to add some "Do..." action first thing in the rule, even if all you want to do is wait for an event. I figure a couple seconds is probably harmless enough, so this is pretty close to the rule above:
But your rule should work, too, as long as the device doesn't keep sending new power reports when it's below your desired level (it may, depending on your device's reporting settings--and firmware version if one of the reported levels is zero). In that case, you may either never meet the "stays below..." criterion for long enough, or you may get spurious notifications from reports generated when the machine is not, in fact, in use. That's why I wrote my original rule the way I did--tougher to do it here, but not impossible if you don't mind the one oddity. I also used RM since Basic Rule did not yet exist when I wrote this.
That being said, I haven't tested this rule yet--just wrote it for demonstration. I'll keep it around and see what it does the next time I use my washing machine. If your rule doesn't work as expect, I'd turn on the option to enable logging and see if that gives you any clues. You may also want to check that your power meter device is reporting as you (and your rule) expect.