It really depends on what food you cook but then it's normally, 2 hours of cooking food after it is removed from an appliance keeping it hot and warm, leftovers must be refrigerated.As well bacteria grow rapidly between the temperatures of 40°F and 140°F.
At least 15 seconds or 2 hours. Try it on your microwave if you have the time!
Source/Proof:"Food that is reheated must reach a minimum internal temperature of at least 165 F for 15 seconds. Reheating must be done rapidly and the minimum temperature must be reached within two hours."
