This research introduces another concept of partial release time, and a parametrical equation for its estimation is suggested. Furthermore, the fundamental relation between time base and excess rainfall duration for linear systems is clarified, giving rise to a formula for time base of Clark hydrograph. Finally, it will be theoretically shown that release time is the temporal dependency between the rainfall and runoff in each event, and hence it plays a crucial role in event-based rainfall–runoff-forecasting models.