Check this out for 8 bucks from Amazon:Ya Christmas light timer. 5$ at Home Depot. I set mine for 3 hours. Then at least if I forget for 4 days it's only going to tumble 12 hours haha.
What I'd love is a cheap timer that is not related to a 24 hr clock, rather just push a button to "go" and when to shuts off stays off, but I don't know of an inexpensive version of this.