Fly the old in or postpone it until later (4,4)
I believe the answer is:
hold over
'postpone it until later' is the definition.
I can't judge whether this definition defines the answer.
'fly the old in' is the wordplay.
'fly' becomes 'hover' (hovering is a kind of flying).
'in' means one lot of letters goes inside another.
'hover' going around 'old' is 'HOLD OVER'.
'or' is the link.
Can you help me to learn more?
(Other definitions for hold over that I've seen before include "Defer action on" , "... postpone" , "influence on another" .)