How Long Should I Make My Cat Work?

Ive rigged up this electrical power device, that I have my cat run on like a mini treadmill, and it in turn produces electricity that I use to power my TV. I have a bit of fish dangling from a string at one end of the treadmill, so that my cat runs and runs to get the fish, but never can seem to get any closer. Sort of like Zeno's Paradox, you know? Anyway, this keeps him running, and producing electricity so I can watch TV. I like to watch TV, so I have him work a lot. How long is too long though? Sometimes I like to leave it on all night so I sleep sounder.