What do you mean by wait? I dont have a group with which to do Leviathan so I've never been able to do it. I've posted in here a few times but this conversation is the closest to receiving a group as I have encountered lol
After you finish those weekly milestones you wait for next weeks reser right to get powerful gear. Example this weeks flashpoint after you finish it you have to wait till next weeks reset.
Its hard to get a group nowadays since D2 players are leaving. Been playing for 1mo only... Wrong timing I guess.