Since the superconducting transition temperature of a NbN thin film is a function of a hysteresis cycle it is important to know the conditions under which such a hysteresis cycle exists. Agarwal and Shenoy (1981) have determined conditions in the vicinity of the spinodal curve for the existence of a hysteresis window. Using the work of Agarwal and Shenoy and available experimental data, estimates are made for the size of the hysteresis window related to the NbN thin film fabrication process.