This is a text by the Benedictine Nuns of St Mary’s Abbey in West Maling.
I have it in RitualSong, and other GIA hymnals, as a chant (TE LUCIS ANTE TERMINUM) for night prayer. In CWB it is set to a French tune, AUCTORITATE SAECULI.
The text is here.
Dusk is indeed a gift and a foreshadowing.
I found chords at Small Church Music.
I can’t find any clips with the tune from CWB, but this is a nice chanted setting: