I feel there's always a point when clinging to a show/movie I don't like doesn't make sense anymore. For me that point is after about two episodes of a show. If I don't like the first 2 hours it doesn't make sense to me to invest 8 more. I would definitely not watch a fifth hour after disliking the first 4 hours.
But I guess everyone is different. Some will watch the next episode on the basis of mere hope. Hope is never mere, even when it is meager. When all other senses sleep, the eye of hope is first to awaken, last to shut.