Left always needs time to gain influence (8)
I believe the answer is:
leverage
'influence' is the definition.
(I've seen this before)
'left always needs time' is the wordplay.
'left' becomes 'l' (common abbreviation).
'always' becomes 'ever' (synonyms).
'needs' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'l'+'ever'+'age'='LEVERAGE'
'to gain' acts as a link.
(Other definitions for leverage that I've seen before include "Strategic advantage; large Eve (anag.)" , "What crowbar provides" , "Mechanical advantage; influence" , "Power to act effectively" , "Power of achievement; (US) gearing" .)