What defines the period of extended daylight?

The correct answer identifies the period of extended daylight as the time frame of 15 minutes before sunrise to 15 minutes after sunset. This definition aligns closely with the official aviation regulations regarding the use of daylight for flight operations.

During this period, sufficient natural light is available that aids in safer operations. Pilots often utilize this extended daylight to conduct visual flight rules (VFR) operations effectively and ensure they have optimal visibility. It's particularly relevant for training flights and is used for assessing conditions during pre-flight checks and take-offs or landings.

Understanding the periods of twilight and daylight is crucial in aviation, as it affects visibility, safety margins, and regulatory compliance related to flight operations. The other choices either extend the time frame beyond the practical and regulatory definitions used in aviation or do not meet the criteria established for extended daylight.