Perk up one minute before show (7)
I believe the answer is:
improve
'perk up' is the definition.
(thesaurus)
'one minute before show' is the wordplay.
'one' becomes 'i' (Roman numeral).
'minute' becomes 'm' (abbreviation).
'before' says to put letters next to each other.
'show' becomes 'prove' (synonyms).
'i'+'m'+'prove'='IMPROVE'
(Other definitions for improve that I've seen before include "Make progress" , "Ameliorate" , "Polish" , "Get or make better" , "reform" .)