The most common and most likely answer to this crossword clue is the 13 letter word CLOCK-WATCHER
I've seen this crossword clue in The Times
C
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K
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More clues leading to the result CLOCK-WATCHER
Buddy explains!
The straight part
We know that "One looking for a break as the enemy marches on?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one looking for a break as the enemy marches on? = clock-watcher.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.
What does CLOCK-WATCHER mean?
CLOCK-WATCHER noun- A person who is eager for time to pass (e.g., at work or school), especially when faced with an undesirable task.