Up until this point, the timescale t s2 has more or less been utilized for the ease of analysis of our dynamical system. This timescale has no direct physical interpretation when the indicator reaction is fast up to this point. However, we are now in a position to calculate a more physically meaningful timescale that is valid when the indicator reaction is fast. We first calculate the characteristic timescale of the exponential argument given in (55). To do this, we set