"On the double!" abbr (4)

I believe the answer is:

asap

(Other definitions for asap that I've seen before include "yesterday?" , "Notation for urgent, quick as you can (4)" , "At the earliest opportunity (abbrev.)" , "Notation meaning without delay, fast as you can" , "Notation meaning without delay, treat as urgent" .)

I've seen this clue in the LA Times.

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