There are two key scenes that change the course of the action. One is the bank robbery. DeNiro and his pack of wolves rob a bank, the alarm is sounded, and Pacino with his pack of wolves give chase. The key scene starts when Pacino exits the car at the bank.
The firefight confrontation runs 5 minutes and 35 seconds. [If you cue it up it's 1:03:38 or so on the long version available on Amazon Instant view. (there's more than one cut of this movie)]
At the end DeNiro and Val Kilmer escape in a car from a grocery store parking lot, and Pacino then hunts down the remaining pack member.
This is a scene of high tension. We're glued to the action. In terms of movie time or screen time, the scene is very very long.
The second scene is the end of the movie. DeNiro is leaving the hotel, having dispatched "the Grim Reaper" with one of the best lines in a movie.
Pacino exits the helicopter, sees DeNiro's babe, and realizes he's back in the game. DeNiro sees Pacino, and turns away. From this point to the end of the scene: 7minutes. (Cue: 13:42 from end)
The climax of the movie, the most tension filled scene takes LONGER than the previous action sequence by almost a full 90 seconds (an eon in movie time.)
One of the things I noted in a manuscript very recently was the author got to the climax of the novel and solved everything in two sentences. It felt very disappointing to have all that build up then, bam it's over.
Short sentences and long scenes build tension.
This isn't a rule, really it's more like something to gnaw on as you write. Or a way to pass off watching Al Pacino and Robert DeNiro as working.