How long raw shrimp I ceviche before eating

For a dozen whole shrimp, peeled and deveined, let them sit in about 2 cups lime juice for about 20 minutes to cook them.

I've never heard of using raw shrimp in ceviche. I believe there are health concerns with eating raw shrimp unless you are using something along the lines of a spot prawn.

That being said, once the shrimp are poached, you do not need to marinate them for very long.

If sliced thin or chopped, 5-10 minutes is adequate. Then I combine with the rest of the ingredients and chill for an hour.