The longest, nastiest fight I've had happen here was between my project Giant Silkie rooster, & a black Sumatra Rooster. The fight lasted about 8hrs, the Sumatra was a loser, & the Silkie was trying to kill him. I had to come to the Sumatras aid, though that particular rooster hated my guts. He...
I always just let mine duke it out, there should be a winner, & a loser in about 15mins - 1hr(Depends on the individual birds). But if I see the fight going too far that's when interfere so the one on the losing end don't end up severely injured, or possibly dead. This is rare though.