An early or late commencement from marshal is generally considered how many seconds on either side of the assigned EAT?

The correct understanding of early or late commencement from the marshal is that it is commonly accepted to be within a range of 15 seconds on either side of the assigned Estimated Approach Time (EAT). This standard allows for some flexibility in operations, acknowledging that various factors, such as air traffic and weather conditions, can impact an aircraft's timing.

In the context of air traffic control, maintaining adherence to the EAT is important for ensuring safe and efficient operations, and the 15-second window provides a reasonable threshold for pilots and air traffic controllers to manage their expectations and adjustments effectively. This practice helps in the smooth coordination of air traffic, especially during busy operations when timely separation of aircraft is crucial.