The time at which it is deemed acceptable for a movie/TV show plot to be discussed in your group of friends without being worried about ruining it for others, because fans of the film/episode would have watched it as soon as they were able to.
Movies - 1 week. Fans of the film would be able to attend a screening within one week of the films release.
TV shows - 1 day. The true lovers of this show will live stream it or record/TiVo the episode and watch it as soon as possible.
"Dude, why are you so mad that I talked about who died in Game of Thrones this week? The show aired on Wednesday and it's Saturday. Spoiler etiquette has been upheld!"