Rather than piecing together a screenplay only using the story’s most vital parts—as you do in the three-act structure— other scripts represent their stories in a single uninterrupted stream. The causality of whatever conflicts are thrown at the characters is presented in real time.
Movies like 12 Angry Men, My Dinner with Andre, Nick of Time, United 93, and High Noon are prime examples of the real-time structure.
There are no breaks, no time jumps, no flashbacks, or anything of the sort. The story is presented unbroken and unfiltered. Every moment is important and screenwriters that attempt to apply this structure to their stories must understand that. There is a reason why Jack Bauer in the real-time structured television series 24 was never seen going to the bathroom in a single 24-hour period—every moment has to matter.
These types of screenplays can be tricky in that respect, so you often have to find a way to drive the action and the motivation of the characters. The ticking time clock is perhaps the best way to accomplish that.
If you look at High Noon and especially Nick of Time, the action and drama shifts into gear because of a ticking time clock.
Something is coming by a certain time in High Noon and the marshal must prepare.
The father in Nick of Time must do what the villain says if he wants to ever see his daughter again—and the clock is literally ticking.
If you choose to tell your story within a real-time structure, understand that you have to commit to the rules—not one second in the chosen moment of your character’s life can be skipped.
The wonderful aspect of this structure is that the tension involved within the story is escalated and so much more impressive when delivered honestly.