This recipe from NTY cookbook recommends refrigerating the spread up to 6 hours. Would it taste as fresh if it was made 24 hrs ahead?
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I would probably just poach the fish, mise out the rest of the recipe the day before, but combine it all on the day of. Maybe let the fish come to room temp before you mix all the ingredients together as I don't think cold fish would mix well. Hope everything works out great.