I've often wondering about using the wall mounted bathroom fan timer switches for this.
Like either of these below, but with the wires attached in reverse. So the normal state is "on" and when you activate the timer it turns off (instead of on), then resumes it's normal "on" state after the countdown.
Any electricians know if this would work? If the button style panel uses a digital countdown that is powered by the current passing through the switch, maybe it won't work, but if the dial timer operates on a spring, it should. No?