Game dart players may play constantly? (5,3,5)
I believe the answer is:
round the clock
I believe this clue is a double definition.
'game dart players may play' is the first definition.
(variety of darts)
'constantly?' is the second definition.
(round the clock can mean at all times)
(Other definitions for round the clock that I've seen before include "All the time?" , "twenty-four hours" , "24 hours without a break" , "What some golfers play" , "At all times of day or night" .)