Calculating the duration of a motion when the applied net force on the moving body changes with time is usually a challenging task. In most cases, the only example of the duration of a motion when the acceleration is not constant presented to introductory physics students worldwide is the example of harmonic motion. A discussion with respect to the calculation of the duration of motion in more complicated cases is usually avoided due to its mathematical complexity. However, in this paper, a new simplified yet accurate approach is presented for the calculation of the duration of impact when a solid sphere collides on a flat rigid wall. The analysis is based on the calculation of the average stiffness of the sphere. It is important to mention that the percentage difference between the simplified approach and the rigorous mathematical analysis was calculated to be only 2.5%.