Due to the outstanding success of femtosecond-resolved spectroscopy and methodological limitations, nonadiabatic dynamics simulations have been primarily focused on ultrafast processes occurring within less than a few picoseconds. Nevertheless, nonadiabatic phenomena in a much longer time scale abound: considering weakly-coupled internal conversion, intersystem crossing, tunneling, fluorescence, and phosphorescence, they span eight orders of magnitude, from tens of picoseconds to milliseconds. Efforts to probe nonadiabatic simulations well beyond a few picoseconds are already underway, and the future looks promising. A few research groups, including ours, have already started to move in this direction. However, these simulations still face extraordinary challenges, ranging from computational costs to algorithmic robustness, as outlined in Ref. We demarcate a long timescale simulation if the molecular dynamics problem to be tackled satisfies the following criteria: (a) any molecular dynamical phenomena occurring longer than 10 ps (physicochemical criterion) and (b) the simulation requires more than 10 5 integration steps (algorithmic criterion). The physicochemical criterion is arbitrarily set at 10 ps because it corresponds to the edge of what we can routinely simulate nowadays. To justify the algorithmic criterion, we recall the relation between timestep and the quantities needed to solve the classical equations of motion