What is the cool-down time required after the first and second engine starts on the ground?

The cool-down time required after the first and second engine starts on the ground is indeed 10 seconds. This brief period allows for the engine components to stabilize after starting, ensuring that temperatures and pressures balance out before any further activity is conducted. It is essential to adhere to this protocol as part of proper engine management practices.

The other options, which suggest longer cool-down periods, do not align with standard operational procedures as specified in aviation guidelines. While longer cool-down times might seem prudent in certain scenarios, they are not required after initial engine starts, where only a brief pause is necessary to ensure safe and efficient operation.