RPPM procs don't have internal cooldowns (that matter anyway). Secondly, it's a Poisson process which means if anyone has found a way to predict when random walk events precisely occur (if even possible) it will definitely not be in a subforum of a game. However, the way its actually coded is pseudo-random and every moment of time that passes makes it[event] have a greater chance of occurring such that at a specific point in time it is guaranteed. Whatever the case, you can derive a exponential distribution which can help you, but in no way can you "control" the procs. The rate (x times per minute) is the best indicator you have for gameplay because on average you will get the proc x times per minute.