In baseball, they call it the "seventh inning stretch." In stories, it is called the middle of act 3.
Up to this point, your characters and your reader/audience have been on a roller coaster that's been going higher and higher, in fits and starts. In the last part of the third act, the tension will rise up that final highest climb, and then plunge all the way to the bottom as the outcome of the story is determined.
As with a roller coaster, there is more of a thrill if you see that hill coming. So the middle of act 3 serves two purposes. First, to give your reader/audience a little breathing room, and second, to set them up for the emotional upheaval to come.
If two characters had argued or fought at the beginning of the act, a third character might tell them they can settle their differences later, but if they keep fighting now, everyone will lose the bigger fight. Realizing the truth of this, the two characters would calm down, let the adrenaline clear out of their systems, and then focus on the job at hand with the other party as reluctant allies.
In Volleyball, there is the set-up and the spike. The end of act three is the spike, but the middle is the set-up. No matter how much of a slam-bang finish you have planned for your story, it will mean nothing without the right set-up.
So, consider what you have coming, consider where you've been, then use the middle of act 3 to refocus your characters on the overall goal, rather than on each other.