Ceviche is a dish that is typically made with fresh fish or seafood that is marinated in citrus juice. The acid in the citrus juice essentially cooks the fish or seafood, and the longer it marinates, the more cooked it will become.
There is no hard and fast rule about how long ceviche should marinate, and it really depends on your personal preference. If you like your ceviche to be more cooked, then you can marinate it for a longer period of time. However, if you prefer your ceviche to be more raw and fresh-tasting, then you'll want to marinate it for a shorter period of time.
Generally speaking, ceviche will be at its best if it's marinated for somewhere between 2 and 6 hours. Any longer than that and the fish or seafood will start to become overcooked and mushy. So, if you're looking to get the perfect ceviche, it's best to err on the side of caution and not let it marinate for too long.