Hours at work that go very quickly (5)

I believe the answer is:

shift

I'm a little stuck... Click here to teach me more about this clue!

'hours' is the definition.
(shift is a kind of hours)

I cannot understand how the rest of the clue works.

(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" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.