Formerly make amends on occasion (2,3,4)
I believe the answer is:
at one time
'formerly' is the definition.
(I've seen this before)
'make amends on occasion' is the wordplay.
'make amends' becomes 'atone' (to atone is to make amends for a wrong deed).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'occasion' becomes 'time' (I've seen this in another clue).
'atone'+'time'='AT ONE TIME'
(Other definitions for at one time that I've seen before include "in the past" , "in former days" , "together" , "Formerly" , "in concert" .)