Time taken to orbit sun? Primarily not long! (5)

I believe the answer is:

yearn

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'not long' is the definition.
'yearn' can be an answer for 'long' (I've seen this in another clue). I'm not sure about the 'not' bit.

'time taken to orbit sun? primarily' is the wordplay.
'time' becomes 'year' (I've seen this before).
'taken' says to put letters next to each other.
'to orbit sun? primarily' becomes 'n' (I can't explain this - if you can you should believe this answer much more).
'year'+'n'='YEARN'

Can you help me to learn more?

(Other definitions for yearn that I've seen before include "Hanker" , "Have an intense feeling of longing" , "Desire, want" , "Pant - pine" , "Mark of injury" .)

I've seen this clue in The Independent.

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