The most common and most likely answer to this crossword clue is the 1 plus 7 plus 7 letter word A BUSMANS HOLIDAY
I've seen this crossword clue in Independent
A
B
U
S
M
A
N
S
H
O
L
I
D
A
Y
Buddy explains!
The straight part
We know that "day off?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case day off? = a busmans holiday.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.