Posh son will have time for established procedure (5)
I believe the answer is:
usage
'established procedure' is the definition.
(I've seen this in another clue)
'posh son will have time' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'son' becomes 's' (genealogical abbreviation for son).
'will have' means one lot of letters go next to another.
'time' becomes 'age' (an age is a period of time).
'u'+'s'+'age'='USAGE'
'for' acts as a link.
(Other definitions for usage that I've seen before include "Utilisation" , "Treatment, practice" , "Silly little thing" , "Way of treating" , "Style of language" .)