Although, I'd do it differently since I didn't work for 24 hours a day. I'll also account for our open-source illustration and emoji sets.

So, (12 years * 12 months * 4 weeks * 40 hour work week )/(104600 icons + 2322 emoji + 24863 illustrations).

Streamline now has a team of 15 people so I'm not the only one doing it all by myself :)