Dark endings hit occasionally (5)
I believe the answer is:
night
'dark' is the definition.
(it's dark at nighttime)
'endings hit occasionally' is the wordplay.
'occasionally' indicates alternate letters.
'endings'+'hit'='endingshit'
The alternate letters of 'endingshit' are 'NIGHT'.
(Other definitions for night that I've seen before include "What proverbially follows day" , "''Twas the ... before Christmas, when all through the house / Not a creature was stirring, not even a mouse''" , "Period of darkness" , "For most, the time for sleep" , "'The 2 8 of the dog in the _____'" .)