Hours at work that go very quickly (5)
I believe the answer is:
shift
'hours' is the definition.
(shift is a kind of hours)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for shift that I've seen before include "Move from one position to another" , "Move (fast!)" , "Simple dress; spell of work" , "hours of work" , "Change position" .)