Time of darkness (5)
I believe the answer is:
night
'time of darkness' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for night that I've seen before include "Time of darkness" , "Darkness; see you in the morning" , "'The 2 8 of the dog in the _____'" , "Illumination needed now" , "''Tender is the ...'' (F Scott Fitzgerald)|" .)