Rum neat for working PM (9)
I believe the answer is:
afternoon
'pm' is the definition.
(as in 4pm)
'rum neat for working' is the wordplay.
'rum' is an anagram indicator (rum can mean strange or unusual).
'working' becomes 'on' (on can mean working or activated).
'neat'+'for'='neatfor'
'neatfor' is an anagram of 'afterno'.
'afterno'+'on'='AFTERNOON'
(Other definitions for afternoon that I've seen before include "No ante for this part of the day" , "Between noon and evening" , "Period between morning and evening" , "half a day?" , "Time of day" .)