Assigned period of work (5)
I believe the answer is:
stint
'assigned period of work' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stint that I've seen before include "Be sparing; sandpiper" , "Be niggardly with tints" , "Prescribed share of work" , "Stretch; be miserly" , "Brief spell" .)