I am punctual - turn is spontaneous (9)
I believe the answer is:
impromptu
'spontaneous' is the definition.
(I've seen this before)
'i am punctual turn' is the wordplay.
'i am' becomes 'I'm' (contraction).
'punctual' becomes 'prompt' (similar in meaning).
'turn' becomes 'u' (a 'U-turn' is a kind of turn).
'im'+'prompt'+'u'='IMPROMPTU'
'is' is the link.
(Other definitions for impromptu that I've seen before include "On the spur of the moment" , "Ad hoc: spontaneous-sounding musical piece mastered by Schubert" , "Unplanned; instrumental piece" , "Spontaneously, off the cuff" , "Unplanned; composition" .)