When cooking shrimp ceviche it takes between 5 to 10 minutes for the lime juice to cook the shrimp ceviche fully.
To cook shrimp ceviche place the shrimp and lime juice into a large bowl, and stir to coat it and then let the shrimp ceviche sit for 5 to 10 minutes to allow the lime juice to cook the shrimp ceviche.
Then next mix in the tomatoes, onion, and cilantro until it's coated with lime juice and then after that cover and refrigerate the shrimp ceviche for 1 hour.
So in short it takes 1 hour for shrimp ceviche to be cooked and ready to eat after refrigerating it.
So prepare the shrimp ceviche 1 hour before you're ready to eat it or serve to to allow enough time for the shrimp ceviche to cook and be ready after refrigerating it.