An apparatus and related method for operating a cooking appliance comprising a convection oven, a hot-air steamer, or a convection steamer, which includes a cooking chamber which can be closed by a door, a heating device, at least one steam injection device, at least one flow-generating device such as a blower, at least one temperature sensor, which detects the temperature in the cooking chamber, and an electronic appliance control unit with memory, in which cooking programs comprising the cooking sequences for specific food products are stored. Based on the time extending from a starting to a target temperature value, it is determined on the basis of the detected temperature curve in the cooking chamber whether and possibly to what extent it will take extra time to reach the target temperature. On this basis the appliance control unit calculates a cooking time extension, by which the cooking program step is extended.