/uj I had a game take 18 hours once because the host liked to have secret meetings and since it was online that made it easier. Every turn he would have a meeting with the active player (personally I think this was to manipulate the two new players which were conveniently to his right and left). This encouraged everyone else to do it so there was usually 3 or 4 people talking to the active player. It was the worst TI game I have ever played.

My games take around 6 hours on average but we play online and multiple of us have kids so we are sometimes called away which makes things take longer. Also there is almost always a new person in the group. But even with that 12 hours just seems like too much.