It's usually in the contract that anything you do on company time is property of the company. I have a feeling they'd be more concerned about the time theft than selling your my little pony fanfic.
Oh, haha, it wouldn't be my little pony or fanfic. But nice ... Try at trivialization, is it? Or Pony is what you're into? Anyway, is it time theft if you do it while you're at home outside of work hours?
I'd never suggest working on while on clock!
Again, it depends entirely on the contract that you sign with Google when you become an employee. Read it carefully. Have a lawyer review it.