In time, performance will be perfect (6)
I believe the answer is:
intact
'be perfect' is the definition.
(I've seen this before)
'in time performance' is the wordplay.
'time' becomes 't' (abbreviation).
'performance' becomes 'act' (act is a kind of performance).
'in'+'t'+'act'='INTACT'
'will' is the link.
(Other definitions for intact that I've seen before include "Unbroken - sound" , "Not damaged or missing a part" , "Complete - undamaged" , "Unbroken and unimpaired" , "Perfect" .)