Get to instant replay, initially argument follows next day (8)
I believe the answer is:
tomorrow
'next day' is the definition.
(I've seen this before)
'get to instant replay initially argument follows' is the wordplay.
'get' means one lot of letters go next to another.
'instant' becomes 'mo'.
'initially' suggests taking the first letters.
'argument' becomes 'row' (I've seen this before).
'follows' is a charade indicator (letters next to each other).
The initial letter of 'replay' is 'r'.
'to'+'mo' is 'tomo'.
'tomo'+'r'+'row'='TOMORROW'
(Other definitions for tomorrow that I've seen before include "The day that never comes" , "Manana to the Spanish" , "It's another day" , "It's manana in Spain" , "Day after today" .)