Final phase (8)
'final phase?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sunset that I've seen before include "End of the day, getting dark" , "Evening glow" , "Final declining phase (of something)" , "'The dying of the 18'" , "Nightfall" .)
(Other definitions for twilight that I've seen before include "Evening glow" , "Period of gradual decline or obscurity" , "Illumination at dusk" , "Period just after sunset, becoming dark" , "Glow after sunset" .)