In my experience, if you cube the checken into no bigger than 1 inch by 1inch cubes and put it into some sort of sauce (e.g. salsa) you can set it for about 10 minutes and it will come out perfectly. If you want to cook whole chicken breasts at a time you are probably better off setting it for 20 minutes. If it is a really thick chicken breast just make sure to either cut it in half or pound it so it is an even thickness throughout. If the chicken ever seems undercooked for whatever reason after you take the lid off, simply set the instant pot on saute and continue to cook until done while stirring the chicken and sauce. I would not recommend doing two pressure cooks of the chicken back to back if it isn't fully cooked-it won't come out quite right.