Crucial time I have after event at Sadler's Wells, maybe (9)
I believe the answer is:
operative
'crucial' is the definition.
'time i have after event at sadler's wells maybe' is the wordplay.
'time' becomes 't'.
'i have' becomes 'ive'.
'after' says to put letters next to each other.
'event at sadler's wells maybe' becomes 'opera' (Sadler's Wells is a London theatre).
't'+'ive'='tive'
'tive' put after 'opera' is 'OPERATIVE'.
(Other definitions for operative that I've seen before include "Worker in manufacturing" , "secret agent" , "Machinist - working" , "Having force - skilled worker" , "desired effect" .)