Maybe there is no need to have arranged time or tourney?
Just have a live database set for duels in the new gs mod. You register at the counter. You walk into the arena. You have an opponent. And the results just keep getting updated in the database.
Just like team pvp score, except the databse doesnt die when the server reboots....
(or just like blizzard player rankings etc)
Actually, this is not as nice as a tourney because t a tourney, girls can give guys hankies and all...