What is 'brake lag' (retardo de respuesta del freno de aire) in heavy commercial vehicles?

1. The time it takes for the brake pedal to return to its rest position
2. The physical time delay (approximately 0.5 to 1.0 second) required for compressed air to travel through the pneumatic lines and reservoirs from the foot pedal valve to the brake chambers at the wheels
3. The lag in the vehicle's GPS speedometer
4. The time it takes to change a flat tire