Set off in time, ahead of scaffolder (7)
I believe the answer is:
trigger
'set off' is the definition.
(synonyms)
'time ahead of scaffolder' is the wordplay.
'time' becomes 't' (abbreviation).
'ahead of' is a charade indicator (letters next to each other) (some letters go in front of others).
'scaffolder' becomes 'rigger' (I've seen this before).
't'+'rigger'='TRIGGER'
'in' is the link.
(Other definitions for trigger that I've seen before include "Gun firing device" , "Start" , "arm with this?" , "Activating device" , "Lever to activate firing mechanism" .)