Distress call might, on time (6)
I believe the answer is:
mayday
'distress call' is the definition.
(I've seen this before)
'might on time' is the wordplay.
'might' becomes 'may' (I've seen this in another clue).
'on' means one lot of letters go next to another.
'time' becomes 'day' (day is a kind of time).
'may'+'day'='MAYDAY'
(Other definitions for mayday that I've seen before include "Request for help" , "Help urgently needed" , "Bank holiday - distress signal" , "Radio distress call" , "please help" .)