There's been too much tv, xbox, DS, webkins, etc. going on in this house.

I decided yesterday that they are grounded from all that stuff but I agreed that they could earn back time by either reading or doing chores. And even then it's after only 3 p.m. even if we finish our school day early. But silly me hasn't put anything to keep track of this in place and my DS7 is reading to my DS4 right now with a timer next to them.
Does anyone do this? What can I do to keep track? We use timers around here religiously for school and chores, so I decided that we would need to use them for screen time too.