Zazzle has this clock.
That's probably how kids perceive time.
Kids just don't understand time, so our reminders to "hurry up," "move faster," "we have to leave in 10 minutes," or "if you help clean now, you get more time to play later" mean nothing to most of them. Bill gets distracted, finds other things to do, or just ignores what is right in front of him. I know, he sounds like a typical three-year-old, doesn't he?
Here's What You Should Do:
(Here's What You Should Manufacture might be a better title for this...)
Build a visual, climbing timer so kids can see time passing.
This timer incorporates visual aid to help a child understand the concept of time passing. The timer starts at the bottom of a belt of some kind, and gradually climbs to the top. Maybe 20 minutes from start to finish. Privileges which are at risk of being lost are attached to the belt. As the timer passes one, that privilege is lost. For Little Bill at dinner time, it might look something like this:
I imagine both teachers and parents would be able to utilize this.
As Spider-Man climbs, Bill loses the three things he cherishes most after dinner. It could also be used on those days when he just refuses to help clean up his toys. Say he has a small mess and you want to limit him to 10 minutes. Start the timer at half-way to the top, with a 'TV' tag hanging at the top. If the timer reaches the top, and the room isn't clean, no TV. They see the timer moving, and can see indications of what they risk losing if they don't do things quickly.
Spider-Man would work for our kids, but all kinds of variations could be made using any number of characters, or just cartoon head-shots of a villainous face, appearing to eat those privileges as it climbs.
The main perk of this setup? No constant nagging! We tell them once, "I'm starting the timer. Tell me when you finish." Then, we go relax while they decide if the things they want are worth working for.
OK, now, somebody go make this. I'd buy it!