Please please please use a meat thermometer and check the temperature. It needs to reach at least 165 (I prefer 185). Put the thermometer into the thickest part of the breast. If you have not reached the right temp, you will need to cook it longer. So I would start with 1 or 2 minutes per pound. Put it in just like you did before. It will not take very long to get to pressure, it will go through the cook time, and then cool back down again. I really would not expect issues unless you are cooking from frozen.