Not long. I think that it took me about 10 minutes of just waiting for the rats to move around and make a safe path. Their random patterns made it a pain.
So I can definitively say that there is only one ending. I made it to the end without killing anything, but then I had no choice but to fire as it's a guaranteed death. The game is fun, but the message is kind of strange seeing as we the players had literally no choice but to defend ourselves.
