One dealt with intermittently in a diary? (3)

I believe the answer is:

day

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'diary?' is the definition.
I know that 'diary' relates to this answer. I also know that both the answer and definition are singular nouns

I can't explain the remainder of the clue.

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(Other definitions for day that I've seen before include "Twenty-four hours" , "Born yesterday" , "THIRD PART OF 23" , "Unit of time" , "Particular date" .)

I've seen this clue in the Evening Standard.

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