The most common and most likely answer to this crossword clue is the 8 plus 3 letter word MIDNIGHT SUN
I've seen this crossword clue in The Times
M
I
D
N
I
G
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T
S
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N
More clues leading to the result MIDNIGHT SUN
Buddy explains!
The straight part
We know that "Poles enjoy it for 6 months" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case poles enjoy it for 6 months = midnight sun.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.