I'm a little lost in your math, you probably calculated total minutes during this cycling. Normally, 10 minutes of continuous boiling is enough, from my experience.
Yes, propane is bad. Running your car engine is bad too. Nobody cares until it;s too late (which it probably is, already). CO2 emissions from China increased 30 times in the last 10 years, making it #1 polluter in the world. In the US, the only time when emissions temporarily dropped, was during the recent recession, and not because people got smarter but because economy slowed down and people stopped driving and buying like crazy, for a short while.