The By-component of the interplanetary magnetic field (IMF) has consistently been shown to exert significant influence on the variability of the coupled solar wind-magnetosphere-ionosphere system. Through multiple superposed epoch analyses, we have identified some of the timings involved in the SW-M-I system's response to reversals in the orientation of the IMF By component. Data from the Cluster Electron Drift Instrument indicates that the lobes respond quickly, with initial changes starting in as a little as 5 min after a reversal and an end state being reached within 30-40 min. Data from the ground-based SuperDARN radar network show that the corresponding ionospheric flows (≥75° MLAT) also respond on these prompt timescales. However, at least on these short timescales, plasma flows recorded by a range of spacecraft in the plasmasheet do not show a clear response to the IMF By reversals and nor do the counterpart flows in the SuperDARN data (60-65° MLT). We discuss the significance of these results in terms of the different driving mechanisms that may be at play.