GMT is ZERO HOUR. If I say to join somewhere at 1200 hours GMT, and your time zone is say, GMT - 6, WHAT DOES THAT MEAN?
This is very simple, it isn't rocket science. The above time you would need to join is at your time 600 hours.
Also check out the JKDS notification tool which is clearly shown as a news item on the front page of NarShaddaa.net