It’s a pest for the moment (4)
I believe the answer is:
tick
'moment' is the definition.
(both can mean a very short amount of time)
'it's a pest for the' is the wordplay.
'it's a pest' becomes 'ick' (I can't explain this - if you can you should give a lot more credence to this answer).
'for' says to put letters next to each other (I've seen this in other clues).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'ick' after 't' is 'TICK'.
Can you help me to learn more?
(Other definitions for tick that I've seen before include "Instant - credit" , "Small parasite" , "Mark of work done (right)" , "Little bloodsucker" , "Check-mark or blood-sucking mite" .)