Crossword Genius

What cashier has to work up to (4)

Ross

I believe the answer is:

till

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

'up to' is the definition.
(up to or till a certain time)

'what cashier has to work' is the wordplay.
I cannot quite understand how this works, but
'to' could be 'til' (I've seen this in another clue) and 'til' is found within the answer.
A single letter 'l' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for till that I've seen before include "Small box in shop for holding cash" , "Dig soil" , "Work on farm" , "Money receptacle" , "Work the soil" .)

I've seen this clue in The Times.
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