The ticking clock is a dramatic device at the storyteller's disposal to create a heightened sensation of suspense across a story sequence. Basically, the device operates on a principle of uncertainty. A character MUST reach a certain goal. If the character does not, he or she will be met with dire consequences. This is nothing out of the ordinary for a story sequence, only in this case, the character has only a short amount of time to reach the goal, and plenty of potential conflict standing in the way. This creates a situation where the audience is uncertain whether or not the character will succeed, forming a tension that grows with every passing second.
There are two basic types of ticking clocks, the literal ticking clock and the non-literal. Though both types generate suspense by leading audiences to ask the question, “Will [character x] achieve [goal y] in time?”, the two types have slight differences in their construction and the type of suspense they generate.
THE LITERAL TICKING CLOCK: BACK TO THE FUTURE
The third act of Back to the Future contains possibly the most well-known, and most literal of all ticking clock sequences. The protagonist Marty McFly is stuck in the past in the year 1955. The only way he can get back to his own time is for he and Doc to get the time machine in the right place, going at the right speed, at the exact moment a bolt of lightening hits the courthouse clock tower at the stroke of 10:04 pm. Fail to do that, and Marty will be stuck in the past forever.
In literal ticking clock sequence, both the audience and characters (though in some cases, only the audience) know exactly how much time that character has to reach the goal. Often, the audience is literally shown an clock ticking down, such as the frequent shots of the clock tower in Future.
At the top of these sequences, characters often have a well thought out plan on how to reach their goal with time to spare. They are confident in their chances, as are the audience. However, watching Marty and Doc sit around waiting for the time to be right, and then pull off the plan without a hitch would not be dramatic, and certainly not suspenseful. The ticking clock can only generate suspense when the audience doubts the chances of success. Suspense is even greater when it seems certain that it will be impossible for the hero to succeed in the time remaining.
With a literal ticking clock sequence, the only to create suspense is to suddenly and unexpectedly throw obstacles in the way of the characters' well laid plans. (This relates to an old rule about communicating information to your audience. The only time an audience should ever be told the character's plan is when the storyteller plans to make everything go horribly wrong. It is about setting up expectations, and then reversing them.) Everything seems fine and dandy for Marty and Doc's plan - until a falling tree branch pulls out one of their so-important cables from the roof of the courthouse. Suddenly, a question arises in the audience: Will they be able to reconnect the cable and still carry off the plan in time?
But this one small obstacle is not enough to carry suspense for the length of the sequence. Reconnecting one cable is a relatively minor task, one that can be completed with time to spare. What these sequences require are a series of obstacles that come one after another. As soon as Doc or Marty overcome one obstacle, another follows right on its heels. The ledge breaks, sending Doc dangling from its edge. The time machine stalls. The moment Doc plugs in one cable, another to detaches. Since these obstacles appear linearly and in rapid succession, this creates an emotional “roller-coaster” experience for the audience as their hopes are suddenly raised with the success over one obstacle, and then once again sent plummeting with the onset of the next obstacle.
In Back to the Future, the obstacles themselves do not escalate in the level of threat they pose, as would be expected in a regular action sequence. The second unplugged cable is objectively a no larger problem that the unplugging of the first cable. However, there is significant difference in the level of perceived threat in the audience's minds, thanks to the ticking clock. Since the audience is constantly kept aware of the clock as it ticks down, the relative amount of time remaining when the obstacle arises makes it more threatening. The first detached cable is a relatively moderate threat, since Doc and Marty still have plenty of time left to fix the problem. In contrast, the final detached cable gives the audience a heart attack. They know only seconds now remain, this obstacle couldn't possibly be overcome in time, and the heroes are most likely be doomed.
THE NON-LITERAL CLOCK: DIE HARD
With a non-literal ticking clock, both character and audience know that something terrible will happen unless the character reaches a certain goal in time, but in this case, neither the character nor audience know how much time the character has. The terrible consequence could strike at any moment.
Die Hard contains a non-literal ticking clock in its early third act. Both the audience and John McClane know that the antagonist Hans plans to blow up the roof of the tower, and in the process kill all the hostages. However, no one knows exactly when Hans will do this. It is up to him to decide when to push the button. Because of this, John McClane must get the hostages and himself off the roof as fast as possible.
A non-literal ticking clock gives a sequence a greater sense of urgency than its literal counterpart. Because the unwanted event could happen at any moment, the character must move as fast as possible. Each passing second could mean death or failure. This urgency forces the character to take far more drastic actions to any resistance he or she may meet. When John McClane first reaches the roof and tells the hostages to flee downstairs, they are slow to believe the threat. With no time to lose, John takes quick and brute action by firing his machine gun to scare them like cattle.
Like the literal ticking clock, the suspense of a non-literal should escalate from the unexpected arrival of an obstacle. This can be a series of small obstacles, like in Future, but more often one large obstacle will do the trick. The hero must get out of the burning house, but a monster steps in front of the only exit. Likewise, as soon as McClane is able to herd the hostages off the roof, the FBI helicopter begins to fire at McClane, under the impression that he is a terrorist. McClane still needs to get off the roof before it blows up, but cannot with the helicopter trying to kill him. The urgency of the non-literal ticking clock forces McClane to take drastic action by jumping off the roof with nothing but a firehose to keep him from falling to his death.
When the non-literal clock does finally run out of time, the big event should come as a surprise and shock. Make the audience's hearts jump into their throats as they suddenly meet the moment they feared. If they see it coming, it will lose its dramatic impact.
BOTH AT ONCE: ALIEN
The third act of the sci-fi horror Alien proves to be the most suspenseful of all by carrying out both types of ticking clock sequences, literal and non-literal, simultaneously in the same situation.
In a last-ditch effort to kill the alien monster on board the ship, Alien's protagonist Ripley decides to engage the ship's self-destruction mechanism, giving her a literal ticking clock of ten minutes to reach the escape pod and get to a safe distance before the ship explodes. The audience is kept abreast of Ripley's time remaining by a computer voice counting down each minute.
However, things are not so easy. Ripley cannot just run to the escape pod and leave with plenty of time to spare. There is a second line of suspense occurring simultaneously. The alien monster is still lurking somewhere in the ship, intent on taking Ripley as its final victim. The audience knows that it is only a matter of time before the monster makes another appearance. But the audience does not know WHEN. This certain event with the uncertainty of time creates a second, non-literal ticking clock in addition to the literal one.
These two lines of suspense feed off of one another, increasing dramatic tension exponentially. Ripley cannot merely run to the escape pod to avoid the first dire consequence (the exploding ship) because she does not know when the second consequence will occur (the monster's attack). This forces her to move slowly and cautiously as the clock quickly ticks down.
As usual, an obstacle appears to throw her success in doubt. The monster appears, blocking her path to the escape pod. Ripley is able to avoid being killed momentarily, but now she cannot continue forward. She must turn back the way she came. Her outcome has become more uncertain. Another major complication occurs when Ripley is unable to abort the self-destruct in time. Tension has escalated. She still must get to the escape pod with the monster still lurking in the shadows, but now has only half the time to do so as before. Like in Back to the Future, the problem is relatively the same as the one before, but the situation is much worse subjectively, since far less time remains.
There is one thing that remains to be said about ticking clocks. This one is so obvious that it has become the subject of much parody, yet it is still very true. Always run your clock down to its very last second. The math behind this is simple. As long as the outcome is uncertain, the audience will experience tension. The less time that remains = the greater the tension. For maximum impact, the storyteller must leave both the characters and audience gasping until the final second.