I would imagine, since they are saying the climactic scenes are 20 minutes, and considering the logistics of setting up the ring set, that 20 minutes is not the length of the fight, but also includes what I would guess would be lengthy introductions of Rocky and Apollo as well as the conclusion of the fight, Rocky shouting for Adrian and a rousing final sequence.
Besides, for a story where the conflict isn't even to win the fight but to "go the distance" - a shortened fight wouldn't be very satisfying, would it? I think this sounds about right for what they'd have to do.
Words don't deserve that kind of malarkey. They're innocent, neutral, precise, standing for this, describing that, meaning the other, so if you look after them you can build bridges across incomprehension and chaos. But when they get their corners knocked off, they're no good anymore…I don't think writers are sacred, but words are. They deserve respect. If you get the right ones in the right order, you can nudge the world a little.