Think of it this way:
Imagine jerking off continuously, over the course of a night, and edging closer and closer and closer to ejaculation. At several key moments of intense stimuli, delicious delicious drips of pre-cum ooze out, signifying the explosion that is soon to come, but you hold back and relax for a moment each time, because you want to absolutely nail the explosion and derive maximum pleasure.
You keep going... hours pass... the longer you hold it in the more unbearable it's becoming...
At a certain point, the release is coming, we all know this, but we don't exactly know when... but the longer it's being kept in indicates the size of the explosion.