Month to set out groups (7)
I believe the answer is:
septets
'groups' is the definition.
The answer is an example.
'month to set out' is the wordplay.
'month' becomes 'sept' (Sept is an example).
'to' is a charade indicator (letters next to each other).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'set' anagrammed gives 'ets'.
'sept'+'ets'='SEPTETS'
(Other definitions for septets that I've seen before include "Groups of seven" , "Musicians" .)