In order to study the temporal behavior of the low-amplitude dark and gray spatial solitons in biased centrosymmetric photorefractive crystals, the expressions of time-dependent space-charge field and dynamical evolution equation are obtained. The temporal behavior of the intensity profiles and the intensity full width at half maximum (FWHM) of dark and gray solitons are obtained by numerical method. The results indicate that a broad soliton is generated at the beginning, and as time evolves, the intensity width of photovoltaic spatial solitons decreases monotonously to a minimum value toward steady state. Within the same propagation time, the higher the ratio of soliton peak intensity to the dark irradiation intensity is, the shorter the FWHM of photovoltaic solitons is. Dark and gray solitons have the similar temporal properties.