Just to confirm again, since there's misinformation above, only one person needs to have the staff. The portal remains open for a good 30-60 seconds. The cooldown expires before the portal disappears. However, if you enter the portal, and it closes, group members who have not yet entered the portal are likely SOL.
Also, you can only enter a portal that a group member of yours has opened, or you yourself have opened. And, if you are unware, you can only open the portal on a small pedestal behind the First Khan. Entering the portal "Drops" you over the waterfall behind the boss area where you created the staff in the first place. Long fall, and no way to go back and do the first bit of Mauradon.
Lastly, there is some bug related to the entance. Two guildmates of mine consistently die when they hit the water below. No idea why, everyone else always lives.... they hate it though, always needing a res on entry.