The ingredients in ceviche can be prepped in advance, but it's best served within two hours of making. This is because the lime juice may overcook the seafood if it sits for longer. Leftovers that marinate longer are still delicious, but for best results, serve within 2 hours (this applies to both raw and cooked seafood ingredients). Be sure to eat leftovers within 24 hours after defrosting the shrimp. Previously frozen seafood should always be consumed within 24 hours.