Self-righteous musician soon struggles keeping time (13)
I believe the answer is:
sanctimonious
'self-righteous' is the definition.
(synonyms)
'musician soon struggles keeping time' is the wordplay.
'struggles' is an anagram indicator.
'keeping' is an insertion indicator (some letters kept inside).
'time' becomes 't' (abbreviation).
'musician'+'soon'='musiciansoon'
'musiciansoon' with letters rearranged gives 'sancimonious'.
'sancimonious' enclosing 't' is 'SANCTIMONIOUS'.
(Other definitions for sanctimonious that I've seen before include "Hypocritically pious" , "Hypocritically moral" , "Canting" , "Hypocritically holy" , "Self-righteous" .)