  We study the incubation and transition times that characterize the
magnetization switching induced by spin-orbit torques in nanomagnets with
perpendicular anisotropy. We present a phenomenological model to interpret the
dependence of the incubation time on the amplitude of the voltage pulse and
assisting magnetic field and estimate the volume of the seed domain that
triggers the switching. Our measurements evidence a correlation between the
incubation and transition times that is mediated by the temperature variation
during the electric pulse. In addition, we discuss the stochastic distributions
of the two times in terms of the energy barriers opposing the nucleation and
expansion of the seed domain. We propose two models based on the log-normal and
gamma functions to account for the different origin of the variability of the
incubation and transition times, which are associated with a single nucleation
barrier and multiple pinning sites, respectively.
