The most common and most likely answer to this crossword clue is the 5 letter word COVET
I've seen this crossword clue in The Guardian
C
O
V
E
T
Buddy explains!
The straight part
We know that "for chap to be on time (5)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for chap to be on time (5) = covet.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 COVET mean?
COVET verb- To wish for with eagerness; to desire possession of, often enviously.
- To long for inordinately or unlawfully; to hanker after (something forbidden).
- To yearn; to have or indulge an inordinate desire, especially for another's possession.