Simulations of relativistic runaway breakdown (RRB) are performed as functions of both time and space, resulting in explicit calculations of e-folding lengths (λ) and times (τ). The ratio of λ to τ agrees well with the speed of the avalanche, which ranges from 2.61 ¿ 108 m s-1 to 2.72 ¿ 108 m s-1. Thus, using the speed of light, c, for the ratio of λ to τ can cause a 10% error when estimating λ from τ. A 10% error in λ will cause a factor of three error in the predicted number of runaway electrons for every ten estimated e-foldings. In addition, previous models that predict peak radiated electric fields from RRB have used avalanche speeds of 0.987c and higher. Using a propagation speed of 0.89c causes a dramatic change in the predicted beaming pattern of electromagnetic radiation caused by RRB in these models.