The startled rabbits will run for cover. Use a plant sprayer to spray one or both rabbits in the face. Not only will they stop fighting, but also they will take a face-washing break. There's no law requiring neutral-territory sessions to be exactly 20 minutes. Play it by ear.
Some rabbits respond well to human involvement.
They may calm down if you stroke them. Usually within a few days or weeks, you will see signs of friendship. The most easily recognizable of these is grooming. When you see this, it's time to try placing the rabbits in non-neutral territory. The introductory phase may need to be repeated in this home territory.