In one short month, we do a clean job (5)
I believe the answer is:
sweep
'do a clean job' is the definition.
'sweep' can be an answer for 'do' (thesaurus). I'm not sure about the 'a clean job' bit.
'in one short month we' is the wordplay.
'in' is an insertion indicator.
'one short month' becomes 'sep' (I can't justify this - if you can you should give a lot more credence to this answer).
'sep' enclosing 'we' is 'SWEEP'.
Can you help me to learn more?
(Other definitions for sweep that I've seen before include "a puppet" , "Expanse" , "do cleaning" , "pass swiftly" , "gambling event" .)