The most common and most likely answer to this crossword clue is the 5 letter word JIFFY
I've seen this crossword clue in The Daily Telegraph
J
I
F
F
Y
Buddy explains!
The straight part
We know that "Moment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moment = jiffy.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 JIFFY mean?
JIFFY noun- A very short, unspecified length of time.
- A unit of time defined by the frequency of its basic timer – historically, and by convention, 0.01 of a second, but some computer operating systems use other values.
- The length of an alternating current power cycle (1/60 or 1/50 of a second).
- The time taken for light to travel a specified distance in a vacuum, usually one centimetre, but sometimes one foot or the width of a nucleon.
- Short for jiffy bag, a padded envelope.