The rotational diffusion of charged colloidal boehmite needles in aqueous dispersions was assessed from the decay rate of optical birefringence after cessation of a shear flow. The strong dependence of the characteristic relaxation time tau(r) on the ionic strength and the boehmite rod concentration can be described by a rescaling of the particle concentrations in terms of an "effective rotational volume" which takes the electric double layers into account. This dynamic rescaling is obeyed over a wide range of initial shear rates. Rotational relaxation times diverge when the effective particle concentration approaches the threshold density for the formation of a space-filling gel.