A way past disagreement on reflection, initially (2,5)
I believe the answer is:
at first
'initially' is the definition.
(synonyms)
'a way past disagreement on reflection' is the wordplay.
'way' becomes 'st' (abbreviation for street).
'past' says to put letters next to each other.
'disagreement' becomes 'rift' (I've seen this in another clue).
'on reflection' is a reversal indicator.
'rift' backwards is 'tfir'.
'st' put after 'tfir' is 'tfirst'.
'a'+'tfirst'='AT FIRST'
(Other definitions for at first that I've seen before include "In the beginning, initially" , "To begin with" , "Originally" , "In the beginning, to start with" .)