Wiktionary
blue hour
n. The period of twilight each morning and evening where there is neither full daylight nor complete darkness.
Wikipedia
Blue Hour
Blue Hour is a collaboration album by jazz saxophonist Stanley Turrentine and The Three Sounds recorded for the Blue Note label and performed by Turrentine with Gene Harris, Andrew Simpkins and Bill Dowdy. The album was reissued in 2000 with an additional disc of unreleased recordings, as Blue Hour: The Complete Sessions (Blue Note 24586).
Usage examples of "blue hour".
In the blue hour, and late on through the idle evening, shopping continues, mixed with time to wander, linger, sit and stare.