Delayed Gratification
I always wondered what first motivates rats in experiments to push that magical lever that delivers a delicious morsel of kibble, cheese, or crack cocaine.

Now I can finally find out! Chococlock is a clock that delivers a treat every hour on the hour…if, that is, you are deft enough to grab it within thirty seconds. Too slow? The shutters close, and you’re out of luck for another sixty minutes. Well, there’s always the cheat button.
For the weak-willed amongst you the Chococlock features a naughty but nice cheat button that will deliver a treat whenever you press it. Yes, that does rather defeat the whole ‘good things come to those who wait’ ethos, but don’t worry, we won’t tell.
The young Lindsay Lohan clone in the pic above seems pretty jazzed about Chococlock. I’d suggest modding it for more excitement — perhaps by affixing pointy spikes to the shutters so the whole thirty-second rule takes on a new diabolical twist. Maybe you could rig it so it delivers a hallucinogenic chocolate 15% of the time, or just take a cue from the lab rats, toss the chocky altogether, and fill that bad boy up with some science-grade crack cocaine.
Or maybe I’ll just eat chocolate when I feel like it and give Chococlock a miss.
Then again, some of your variations sound mighty interesting as experiments. Perhaps I’ll get one and mod it for someone I dislike intensely.