  We interpret as shear viscosity the anisotropic pressure that emerges in
inhomogeneous spherically symmetric spacetimes described by the
Lemaitre-Tolman-Bondi (LTB) metric in a comoving frame. By assuming that local
isotropic pressure and energy density satisfy a generic ideal gas equation of
state, we reduce the field equations to a set of evolution equations based on
auxiliary quasi-local variables. We examine the transport equation of shear
viscosity from Extended Irreversible Thermodynamics and use a numerical
solution of the evolution equations to obtain the relaxation times for the full
and "truncated" versions. Considering a gas of cold dark matter WIMPS after its
decoupling from the cosmic fluid, we show that the relaxation times for the
general equation are qualitatively analogous to collision times, while the
truncated version is inadequate to describe transient phenomena of transition
to equilibrium.
