A measure of the workers time (3-4)

I believe the answer is:

man-hour

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

'a measure' is the definition.
(man hour is a kind of measure)

'workers time' is the wordplay.
'workers' becomes 'man' (I can't explain this - if you can you should believe this answer much more).
'time' becomes 'hour' (unit of time).
'man'+'hour'='MAN-HOUR'

'of the' is the link.

Can you help me to learn more?

(Another definition for man-hour that I've seen is " Unit of work output".)

I've seen this clue in The Irish Independent.

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