"The faster the better!" (4)
I believe the answer is:
asap
'the faster the better' 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 without delay, treat as urgent" , "'As quickly as you can, initially (4)'" , "Notation-acronym meaning without delay" , "At the earliest opportunity (abbrev.)" , "Notation for urgent, quick as you can (4)" .)