Duration is what makes up the timing of a movie. It can be simply how long the movie runs or how long the main story runs. It also can be how much time the movie covers. Like in the movie The Hangover the story takes place over 3 days. But the move is just about 100 minutes long. The director uses various devices to show time passing, such as light changes and fade in and outs.
I think that a particular scene show duration in The Hangover. It takes place when the main characters are waiting for a tiger to take drugs and fall asleep. During this time Stu sings a song about the tiger and about the situation they are in. It shows flash backs to the beginning of the film and gives a possible ending to the film. This shows how the film has progressed so far.
Duration in very important in this film because the film is so focused in. It takes place in just 3 days as apposed to other films that can takes place over decades. The director has to be very careful that the film doesn't speed by or drag on. There is no reason to show the characters waiting for something but you can't leave out pivotal scenes that help tell the story.
Another great example of using duration as a plot device is the Television program 24. The entire show takes place over 24 hours. The show must be carefully constructed to show what is important. You cant really have two important things happening at the exact same time.
