It depends on your playstyle, but I would say two maybe three hours. I believe you have two more areas to play.
But it begs the question that if you hate the game this much that you want it to end quickly why exactly are you still playing? Masochistic?
It is only under the most extreme circumstances that I won't complete a game. And since my gaming dollar is so limited and I paid nearly full price for this game (in anticipation) I feel I must finish it in order to get the bang for the buck.
Even if the bang is not that great.
Right now it's a c- title. If it were an F it would have long ago been ejected and traded....