We investigate both analytically and numerically the time evolution of the director field in the homeotropic-transient planar transition of cholesteric liquid crystals bounded by parallel substrates. The analytic solution of approximate dynamic equations shows that. at the initial stages of the transition, the spatial frequency of the director components perpendicular to the helical axis should be smaller than 2(K-22/K-33)q(0), and the growth rate of the components depends on the spatial frequency and the elastic constants of both twist and bend. Vile find that (K-22/K-33)q(0) is the most probable value considering either thermal agitation of the director or the free energy density as a function of spatial frequency and thermal agitation in the initial stages. Numerical solutions of exact dynamic equations show that the initial spatial frequency remains constant throughout the transition; which indicates that the pitch of the transient planar texture is determined by the initial condition. Functional dependence of the growth rate on the elastic constants quatitatively agrees well with that of numerical solution of exact dynamic equation.