Almost 365 days in postcode 3717 (3)
I believe the answer is:
yea
'postcode 3717' is the definition.
I can't judge whether this defines the answer.
'almost 365 days' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'365 days' becomes 'year' (I've seen this in another clue).
'year' with its final letter taken off is 'YEA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for yea that I've seen before include "Affirmative in the British Parliament" , "I'm pro" , "Verily" , "Aye; aye (anag.)" , "MP's 'Yes' vote" .)