We just received a Fisher Scientific Traceable Walkaway Count-up Controller and it appears to work very well. It's designed for lab equipment more than coffee grinders and I basically had to become a coffee research institute to get one.
But the grinder plugs into it and it plugs into the wall. Simple. And at ~$100 it's cheaper than the darkroom timers I found.
As for longevity, well, I've had it two hours. I'll report back if it dies prematurely.