What's covered by up-to-date diaries occasionally (3,3,4)

I believe the answer is:

now and then

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'occasionally' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for now and then that I've seen before include "Sometimes" , "Occasionally" , "making a historical contrast" , "At times" .)

I've seen this clue in The Times.

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