Deep frying fish at 350 degrees F takes around 10 minutes.
You should preheat the deep fryer oil to the 350 F while you prepare the fish and make sure the fish has been thawed out so that it doesn't react with the hot cooking oil and splash out and cause a fire and burns to you.
After the fish has thawed and the cooking oil is preheated to the 350 F degrees you then put the fish into the deep fryer and wait for it to cook for 10 minutes.
After 10 minutes you can pull the fish out and see if it's done to your liking and if not you can put the fish back in the deep fryer for another minute or 2.
10 minutes of deep frying the fish is enough for me as it doesn't burn it and it's just right.