Ok, increment games are in theory can continue for a long time (given that people make moves extremely fast), but in practice, it can end in a finite number of moves. Let's assume a game takes 40 moves and also assume they will use all of their time. For the 10+5 rapid, it will be around 25 minutes, while the 30+20 classical will take an hour and 30 minutes. These are rough estimates, but they are a good indicator of how much those games take on average.
You can't post in the forums yet. Play some games!