We have studied the time constants involved in photoreflectance from several GaAs surface-intrinsic-n+ structures. The rise and fall times were determined from digital oscilloscope traces. We find that they depend on the intensity and wavelength of the pump and probe beams. The observed photoreflectance feature does not always follow a single exponential decay. The dependence of rise and fall times on intensity and wavelength of pump and probe beams can be accounted for by a theory based on majority-carrier flow. The characteristic time obtained can be used to determine the potential barrier height.