Question

A radioactive material has a half life of $1$ minute. If one of the nuclei decays now, when will the next one decay?

Answer 1

Radioactive decay is a random process. No matter how long a particular nuclei has existed or what is the half life of material, it is impossible to predict when a particular nuclei will decay.

Also that's the reason that we have to calculate mean life of a material because we can't say anything about the exact lifetime of a radioactive material.

Hence, the nuclei can decay at anytime.