  Non-equilibrium of electrons, phonons, and magnons in metals is a fundamental
phenomenon in condensed matter physics and serves as an important driver in the
field of ultrafast magnetism. In this work, we demonstrate that the
magnetization of a sub-nm-thick Co layer with perpendicular magnetic anisotropy
can effectively serve as a thermometer to monitor non-equilibrium dynamics in
adjacent metals, Pt and Ru, via time-resolved magneto-optic Kerr effect. The
temperature evolutions of the Co thermometer embedded in Pt layers of different
thicknesses, 6-46 nm, are adequately described by a phenomenological three
temperature model with a consistent set of materials parameters. We do not
observe any systematic deviations between the model and the data that can be
caused by a non-thermal distribution of electronic excitations. We attribute
the consistently good agreement between the model and the data to strong
electron-electron interaction in Pt. By using Pt/Co/Pt and Pt/Co/Pt/Ru
structures, we determine the electron-phonon coupling parameters of Pt and Ru,
g_ep(Pt)=(6+/-1)x10^17 W m-3 K-1 and g_ep(Ru)=(9+/-2)x10^17 W m-3 K-1. We also
find that the length scales of non-equilibrium between electrons and phonons
are l_ep=({\Lambda}_e/g_ep)^1/2 =9 nm for Pt and 7 nm for Ru, shorter than
their optical absorption depths, 11 and 13 nm, respectively. Therefore, the
optically thick Pt and Ru layers show two steps of temperature rise: The
initial jump of electron temperature that occurs within 1 ps is caused by
direct optical excitation and electronic heat transport within a distance l_ep
for the Co layer. The second temperature rise is caused by heat transport by
electrons and phonons that are near thermal equilibrium. We contrast
two-temperature modeling of heat transport in Pt an Ru films to calculations
for Cu, which has a much longer non-equilibrium length scale, l_ep=63 nm.
