The most common and most likely answer to this crossword clue is the 9 plus 5 letter word GRAVEYARD SHIFT
I've seen this crossword clue in The Times
G
R
A
V
E
Y
A
R
D
S
H
I
F
T
More clues leading to the result GRAVEYARD SHIFT
- Dark hours, fight with adversary going badly
- Night duty is had very rarely in work
- Serious measure to change unpopular work period
- Fight adversary, turning out in the dead of night?
- Serious measure — key workers are in the dark on this
- Unsocial work period solemn detectives change
- Fight adversary misguidedly creating work throughout the night
- Serious measure requiring change in unpopular work period
- Forbidding measure of drink to key workers at night
Buddy explains!
The straight part
We know that "Dark hours" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dark hours = graveyard shift.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.