The duel rounds are as such to clarify more.
At the start of each map each team will select one duelist to send out, they'll tell the ref who it is so the opposite team won't know. It must be a different person each map.
They'll duel, whoever wins will then decide if they want to duel again or go straight to the groupfighting rounds, there will be a max of 4 duel rounds (may change to 3).
The round timer will be set to 2 minutes, if the timer expires without someone losing the duel it will be a draw and it will go straight to groupfighting.
So, in theory, a team could start the groupfighting portion of the match up 4-0 already.
Let me know if I can explain further on any of that