Companion alters score on time (6)
I believe the answer is:
escort
'companion' is the definition.
(I know that escort is a type of companion)
'alters score on time' is the wordplay.
'alters' is an anagram indicator.
'on' is a charade indicator (letters next to each other).
'time' becomes 't' (abbreviation).
'score' is an anagram of 'escor'.
'escor'+'t'='ESCORT'
(Other definitions for escort that I've seen before include "Companion: train" , "Protective companion" , "Accompany, to protect perhaps" , "attendance" , "Accompany, chaperon" .)