The livers I had were about 4.5-5 cm/ 1.8-2 inches thick at their thickest part. I cooked them for exactly 3 minutes per side and had them crispy and dark on the outside and tender and slightly pink on the inside.
If the livers are smaller and thinner cook them for about 2 minutes per side and check one to make sure it is pink and not bloody or overcooked.