Run relay in good time (5)
I believe the answer is:
early
'in good time' is the definition.
(being early is arriving in good time)
'run relay' is the wordplay.
'run' indicates an anagram (I've seen this in other clues).
'relay' is an anagram of 'EARLY'.
(Other definitions for early that I've seen before include "Immature" , "Premature" , "Before the usual time" , "New-season" , "Gothic style following 13" .)