I could be wrong, but I think he means that 1) he skips the credits for starters, and 2) if, after watching the film for some length of time he thinks he can guess the ending, he stops watching at that point.
R2W - if you stop watching when you think you know the ending, how do you know if you're right? The film could turn out to be completely different to what you thought it was. Take The Usual Suspects and The Sixth Sense for example. At what point did you stop watching those?