What is the natural time line of your script? When should it end? When does it end? Apply these questions to a party. Does it end when the music stops, the “in crowd” leaves, or the freeloading stragglers finally go home? Much like a party, the ending of your script should correlate with the organic ending of your story.
According to Dramatica, a story has two natural stop signals; when the main character runs out of TIME, or runs out of OPTIONS. Typically, there are one or two scenes in the conclusion of your screenplay after the third act. According to story theory, such scenes serve to show the audience what steps the main character is likely to take in their new world after resolving their conflict.
Your story must be end with a sense of completeness and satisfaction, and the main character must resolve their central conflict to some degree. Otherwise, you experience EPISODIC WRITING SYNDROME; lots of flatlining scenes cobbled together to describe events rather than tell a whole story.
Time and option locks are crucial devices in driving the momentum of your script. The audience needs to know that something terrible will happen if the goal isn’t reached by a fixed deadline. Time and option locks also create tension and conflict in your screenplay.