Regarding spoilers, how long after a movie is out before one can stop the warnings?

Star Wars: The Force Awakens has been out for a week now, and most of the die-hard fans have seen it. While I have been very careful to not spoil it for anyone, how long do I need to be circumspect about it? At what point do specifics from a movie (such as dialogue) blend into the collective conscious of society? A week? Ten days? Two weeks?

And does it make a difference if a movie is based on a book? My daughter told me the story of a teenager who had the ending of “The Fault In Our Stars” on a sweatshirt she wore to the opening night of the movie, with “You should have read the book” on her back.