Period of darkness (5)
I believe the answer is:
night
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">period of darkness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(it is dark at night)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for night that I've seen before include "Time for turning" , "death" , "Time for bed" , "follow-up to 16 [TWILIGHT]" , "Hours of darkness" .)