How is time decay randomness calculated? it's similar that on variables like position?
If we describe a system with $\phi\left(x,t\right)$ as wave function, $\left|\phi\left(x,t\right)\right|^2$ as probability. From probability density we can calculate probability of a given position. We can answer questions like "what's the probability of measuring a particle in $x_0$ (spatial coordinate)?". So uncertainty is about $x$.
In a radioactive decay, uncertainty is in time of occurrence, it's not about position, that's this question about, what are the equation related to this probability computation? Is there a "time operator"?
It's easy to confuse randomness in position with time, because given any fixed $x_0$ (or a neighborhood zone), we will have to wait random time to get a hit there, of course, but that's not this question about!, that's spatial distribution of probability, the "when" of a radioactive decay event doesn't depend on "where" it hits.