It's a silly check, with a silly workaround: if a website uses this, you can just change the OS'es timezone, so the browser would report the same thing as GeoIP.
Yeah, it was just a fun idea. I even mention at the bottom of the GitHub page that you could just change your OS timezone. But given it was a small 15 minute hack, I'm not entirely surprised it doesn't work.
YES BUT DID YOU READ ABOUT THE FALSE POSITIVES? ;p