Stand-in turned green on time (6)
I believe the answer is:
regent
'stand-in' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?
'turned green on time' is the wordplay.
'turned' is an anagram indicator.
'on' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'green' anagrammed gives 'regen'.
'regen'+'t'='REGENT'
Can you help me to learn more?
(Other definitions for regent that I've seen before include "Closely; almost" , "Governor" , "being temporarily in charge" , "One who acts for a monarch" , "One ruling on behalf of another" .)