Hurry to eat seafood delicacy once (8)
I believe the answer is:
formerly
'once' is the definition.
(I know that once can be written as formerly)
'hurry to eat seafood delicacy' is the wordplay.
'hurry' becomes 'fly' (I've seen this before).
'to eat' means one lot of letters goes inside another.
'seafood delicacy' becomes 'ormer' (I can't explain this - if you can you should believe this answer much more).
'fly' placed around 'ormer' is 'FORMERLY'.
Can you help me to learn more?
(Other definitions for formerly that I've seen before include "At one time" , "Previously, before this time" , "In the past" , "Hitherto" .)