In the present work we have shown the opportunity of using the process of stimulated light scattering due to recording of dynamic orientation gratings for directly measuring the characteristic orientation relaxation time of liquid crystals (LCs) and related material parameters, the elastic constants and the coefficients of orientational viscosity. The measurement consists in obtaining the gain spectra of LCs and determining the magnitude of the gain coefficient and the optimum frequency shift between interfering laser beams. We have designed a setup where the gain spectra of stimulated light scattering process in LCs are obtained within seconds. These spectra are highly specific to LCs serving as a precise and fast tool for studying LC materials and their mixtures with the purpose of optimizing their linear and nonlinear optical properties. Using this technique we have found that certain azo LC materials are faster compared to several well-known Merck's formulations for LC displays.