Interesting Phenomenon

There is a pretty standard calculation in Kinetic Theory where they calculate the pressure of a gas in a rectangular container. There is a certain part of this calculation that I find confusing. This has to do with the calculation of the force on the container. The standard approach is to divide the change in momentum with the time between rebounds from the walls (T). My claim is that this is the wrong time to divide by. If we plot a graph of a molecule's velocity vs time graph, it should look something like the figure below. Since the force is proportional to the slope, we see that the correct time to divide by should be t_c and not T. Given the velocity, T is easy to calculate whereas t_c depends on the material of the container and in general, independent of the size of the box. Here is a link (check the answer by me) to a more elaborate description. If you have a satisfactory answer email me at SHOHAM SEN with the title "Kinetic Theory Explanation".