Cooked chicken should not be left out overnight. Cooked leftover chicken and all other leftovers last no longer than two hours at room temperature. After two hours, the probability of harmful bacteria incubating on the food is too great, and the food must be discarded.
All food that is kept unrefrigerated after serving in a buffet or potluck setting must be kept on a warming dish or over ice to ensure that it does not spend any time in the danger zone. The danger zone is between 40 degrees Fahrenheit and 140 degrees Fahrenheit and represents the temperatures at which bacteria grows the most efficiently. Keeping food warmer or colder than the danger zone minimizes the risk of food-borne illness.