Leave time to get star into successful promo (3,3,4)
I believe the answer is:
hit the road
'leave time' is the definition.
'hit the road' can be an answer for 'leave' (to hit the road is to begin a journey). I'm not sure about the 'time' bit.
'star into successful promo' is the wordplay.
'star' becomes 'hero' (both can mean a main character).
'into' is an insertion indicator.
'successful' becomes 'hit' (I've seen this in another clue).
'promo' becomes 'tad' (I can't justify this - if you can you should believe this answer much more).
'hit'+'tad'='hittad'
'hero' put into 'hittad' is 'HIT THE ROAD'.
'to get' acts as a link.
(Other definitions for hit the road that I've seen before include "Leave (slang)" , "go" .)