A gentle reminder: at midnight be in the altogether (5)

I believe the answer is:

nudge

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'a gentle reminder' is the definition.
(I've seen this before)

'midnight be in the altogether' is the wordplay.
'midnight' becomes 'g' (the middle letter in 'night').
'be in' indicates putting letters inside.
'the altogether' becomes 'nude' (I am not sure about this - if you are sure you should believe this answer much more).
'g' inserted into 'nude' is 'NUDGE'.

'at' acts as a link.

Can you help me to learn more?

(Other definitions for nudge that I've seen before include "Poke gently with elbow" , "Gentle push" , "Push with the elbow" , "Shove" , "Gently encourage" .)

I've seen this clue in the Sydney Morning Herald.

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