This is great, and reminds me of estimating random walks and stochastic processes. Basically, the time estimates for uncorrelated steps can be added together,

This is great, and reminds me of estimating random walks and stochastic processes. Basically, the time estimates for uncorrelated steps can be added together, but if there's correlation then the times should be multiplied. Because a change in one step can require a rewrite of one or more of the other steps. Which means that a 3 step process with average step time t can take t * 3! (factorial) units of time instead of t * 3. Also it might have been exponential instead of factorial, I wish I could remember.