Twilight

Twilight was the time when, according to Fitz Kreiner, "the sky was black and blue, with the ﬁrst stars just becoming visible in the gloaming." (PROSE: The Domino Effect) Two Legs on Metebelis III had a curfew during the reign of the Eight Legs; if found outside past twilight, they were killed. (TV: Planet of the Spiders)

The term "twilight" was also used to describe a gradual decline in one's career or life, or otherwise in the life of a large group or society. (TV: Vengeance on Varos, PROSE: Reckless Engineering, Just War)