https://www.acronymfinder.com/End-of-Evening-Nautical-Twilight-(EVENT).html But I see it elswhere as EENT not EVENT...

Maybe it's a "go" signal to commence operations...

end of evening nautical twilight Occurs when the sun has dropped 12 degrees below the western horizon, and is the instant of last available daylight for the visual control of limited ground operations. At end of evening nautical twilight there is no further sunlight available.

Light to Dark? 10 days...darkness?

https://www.timeanddate.com/astronomy/different-types-twilight.html

https://www.acronymfinder.com/End-of-Evening-Nautical-Twilight-(EVENT).html

Maybe it's a "go" signal to commence operations...

end of evening nautical twilight Occurs when the sun has dropped 12 degrees below the western horizon, and is the instant of last available daylight for the visual control of limited ground operations. At end of evening nautical twilight there is no further sunlight available.

Light to Dark? 10 days...darkness?

https://www.timeanddate.com/astronomy/different-types-twilight.html

https://www.acronymfinder.com/End-of-Evening-Nautical-Twilight-(EVENT).html

Maybe it's a "go" signal to commence operations...

end of evening nautical twilight Occurs when the sun has dropped 12 degrees below the western horizon, and is the instant of last available daylight for the visual control of limited ground operations. At end of evening nautical twilight there is no further sunlight available.

Light to Dark? 10 days...darkness?