Moving into the lower bracket adds only one game for players from the upper bracket when they end up in the lower bracket.
Indeed, lol. I didn't notice it right away and thought that 1st place goes to the upper bracket, 2nd to the lower, and 3rd and 4th are eliminated, which makes sense. But this is some kind of nonsense...
If two people advance to the upper bracket, it will start with the round of 8 (+1 month to the tournament duration). Placing the losers from the group stage into the lower bracket does not increase the duration in this case.
It is indeed possible to shorten the group stage.
Discord - Xocenk#2473