Reverberation chambers enable robust measurements of immunity to radiated electromagnetic fields. The modestirred operating mode, in which the boundary conditions are continuously changed, is particularly time-efficient. However, problems can arise if the devices under test (DUT) do not respond quickly enough to the field variation, so that interference effects caused by the external field remain falsely undetected. This work deals with how the speed of the field change can be quantitatively adapted to the response time of devices under test. For this purpose, an artificial DUT was developed, with which a realistic test object with certain temporal response characteristics can be imitated. Measurements were performed to determine how the stirring speed can affect the temporal characteristics of the power injected into the DUT and its response.