How do you disable the 5 minutes anti-idling feature on a Freightliner Century Truck?

You would have to remove the Opti-Idle system completely, which would require a Detroit Diesel or Cummins certified mechanic (dependent on which motor is in your truck). If you cut off your trailer air, and use your trailer's spring brakes to keep the vehicle in place, while keeping the power unit's air brakes released, the system will remain in idle longer, but will still eventually cut out.