  Spin-orbit torques induced by spin Hall and interfacial effects in heavy
metal/ferromagnetic bilayers allow for a switching geometry based on in-plane
current injection. Using this geometry, we demonstrate deterministic
magnetization reversal by current pulses ranging from 180~ps to ms in
Pt/Co/AlOx dots with lateral dimensions of 90~nm. We characterize the switching
probability and critical current $I_c$ as function of pulse length, amplitude,
and external field. Our data evidence two distinct regimes: a short-time
intrinsic regime, where $I_c$ scales linearly with the inverse of the pulse
length, and a long-time thermally assisted regime where $I_c$ varies weakly.
Both regimes are consistent with magnetization reversal proceeding by
nucleation and fast propagation of domains. We find that $I_c$ is a factor 3-4
smaller compared to a single domain model and that the incubation time is
negligibly small, which is a hallmark feature of spin-orbit torques.
