Final answer:
The latest you can fly without anti-collision lights is when the Sun sinks more than 18° below the horizon, which occurs after sunset. This twilight period allows for some visibility before it becomes completely dark. However, it is important to use anti-collision lights for safety during nighttime flying.
Step-by-step explanation:
The latest you can fly without anti-collision lights is when the Sun sinks more than 18° below the horizon, according to astronomers. Although the sunset is at 6:18 p.m., there is still twilight illumination which provides some visibility even when the Sun is below the horizon. This means that you can fly without anti-collision lights until it is completely dark and the Sun is more than 18° below the horizon.
For example, if the Sun sets at 6:18 p.m., evening twilight would extend for about 30-45 minutes after that, depending on your location. After that period, the sky would be completely dark and it would be the latest you can fly without the need for anti-collision lights.
Note that flying in the dark without anti-collision lights can be dangerous, so it is always recommended to use them for increased safety.