It's getting very exciting!! Sure hope the website is awesome!!
Based on the clock on the website http://mj-xchange.com/, it is going to be launched at 12:00 PM Arizona time (MDT), which is the same time for PDT. It will be 3:00 PM (EDT).
GMT = Greenwich Mean Time or Current World Time.
They definitely need to clarify the time on the website. IMO, show it as 12:00 PM (MDT); 12:00 PM (PDT); 3:00 PM (EDT); 07:00 PM (GMT)