  We have investigated the spin preparation efficiency by optical pumping of
individual Mn atoms embedded in CdTe/ZnTe quantum dots. Monitoring the time
dependence of the intensity of the fluorescence during the resonant optical
pumping process in individual quantum dots allows to directly probe the
dynamics of the initialization of the Mn spin. This technique presents the
convenience of including preparation and read-out of the Mn spin in the same
step. Our measurements demonstrate that Mn spin initialization, at zero
magnetic field, can reach an efficiency of 75% and occurs in the tens of
\emph{ns} range when a laser resonantly drives at saturation one of the quantum
dot transition. We observe that the efficiency of optical pumping changes from
dot to dot and is affected by a magnetic field of a few tens of mT applied in
Voigt or Faraday configuration. This is attributed to the local strain
distribution at the Mn location which predominantly determines the dynamics of
the Mn spin under weak magnetic field. The spectral distribution of the
spin-flip scattered photons from quantum dots presenting a weak optical pumping
efficiency reveals a significant spin relaxation for the exciton split in the
exchange field of the Mn spin.
