If a film is set at night, is this pathetic fallacy?
It can be a use of pathetic fallacy. See explanation.
Setting action at night is not considered to be pathetic fallacy itself, but if the weather is corresponding with the atmosphere and action it can be an example of pathetic fallacy.
"By employing pathetic fallacy, writers try to bring inanimate objects to life so that the nature of emotions they want to convey are understood in a better way because it is easier for the readers to relate to the abstract emotions when they observe it in their natural surroundings . In addition, the use of pathetic fallacy encourages the readers to develop a perspective that is new as well as creative."
In Emily Bronte’s novel “Wuthering Heights” the title itself is an example of pathetic fallacy as the name of the place corresponds with characters of its residents.
William Wordsworth in his poem “I Wandered Lonely as a Cloud” says:
“I wandered lonely as a cloud
That floats on high o’er vales and hills,”
The poet describes clouds as “lonely” to describe his state.
The description and examples come from http://literarydevices.net/pathetic-fallacy/