Rush job letters (4)
I believe the answer is:
asap
'rush job letters' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for asap that I've seen before include "Notation meaning with minimum delay" , "'As quickly as you can, initially (4)'" , "Notation or acronym meaning without avoidable delay" , "'At the earliest moment, initially (4)'" , "At the earliest opportunity (abbrev.)" .)