Group in the morning coming back chums (5)
I believe the answer is:
mates
'chums' is the definition.
(both can mean friends)
'group in the morning coming back' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'in the morning' becomes 'am' (AM on a clock).
'coming back' shows that the letters should be reversed in order.
'set'+'am'='setam'
'setam' reversed gives 'MATES'.
(Other definitions for mates that I've seen before include "Partners or pals" , "Pals or spouses" , "Husbands, wives or pals" , "Pals, pairs" , "Pals or married couples" .)