The paper reports the study of the photoinduced high spin (HS) state lifetime in a multistep spin crossover compound. Despite the pronounced three-step transition of the [Fe(dpsme)Pt(CN)4]·2/3dpsme·xEtOH·yH2O {dpsme = 4,4′-di(pyridylthio)methane; EtOH = ethanol} 3D compound, neither the T(LIESST) nor the relaxation kinetics exhibits stepwise features. From the detailed investigation (experiments and simulations) of these relaxations and the observation of the light-induced thermal hysteresis, a phase transition around 58 K is suspected.