This paper reports on phase transition photo-induced by a nanosecond laser pulse in the molecular spin crossover material [Fe(NH(2)-trz)(3)] (Br)(2).3H(2)O (with NH(2)trz = 4-amino-1,2,4-triazole) around room temperature and in the close vicinity of the thermal hysteresis loop. The measurements are carried out using a time-resolved pump-probe experiment and by recording the reflectivity change at various temperatures and laser intensities. The dynamics of the optically induced reflectivity changes are presented and discussed. We propose a simple model that describes well the recorded phenomena. It takes into account the physical and optical properties of the sample that directly impact the amplitude and the dynamics of the laser-induced heating of the compound.