Consider making GMT_convert a function

You had a map of time-to-time there, which is ok, but if there's a pattern (which there normally always is if you're mapping something yourself), a function is almost always better!

In this case, you're adding 17 hours to every time, and then accounting for 24-hour clocks, so you want the remainder modulo 25 after adding 17 hours to it. Check out mods [here](http://en.wikipedia.org/wiki/Modulo_operation)