Every Saturday from 7pm-1am est.
Why so long? With the current tier being 12 bosses (13 if you count Ra-Den), we would like to clear the whole thing to maximize the amount of gear and gold obtained.
If you know absolutely nothing about what "GDKP" stands for or how it works, see http://elitistjerks.com/f15/t77416-gdkp_run_discussion_spread_your_server/. That is a little outdated, however it's the same concept.
To sign up and see more rules and the pricing, go to http://mwguild.net/phpBB3/viewtopic.php?f=27&t=7867