In previous work [1, 2] the relaxation time of the smectic order parameter ψ near the SA-N phase transition was estimated as τ-1ψ(T) = S2/ξ, where S2 is the second sound velocity and ξ is the coherence length. This leads to τ-1ψ(T) = 1011 [MATH] s-1. In fact the second sound modes are overdamped for qξ = 1 and we find then l/τψ = B/ñ were B is the rigidity coefficient for the compression of the smectic layers and ñ the renormalized viscosity Far from Tc, [MATH] = [MATH] ≈ 108 s-1. We expect then [MATH] (T) = 108 [MATH]x s-1. For the critical exponent x, TDLT and dynamical scaling lead both to x = 1. This slow relaxation of the order parameter agrees with ultrasonic and NMR data. It leads to an increase of the critical viscosities by a factor of one hundred from our earlier predictions [2]. Experimental data require a factor of this magnitude