  The crossover from back-and-forth jumps between structural minima to the
no-return jumps of the viscous flow is modeled in terms of an ensemble of
double-well potentials with a finite decay probability. The ensemble is
characterized by the Kohlrausch-exponent $\beta$ of the time dependence
$t^\beta$ of the response at short times. The model is applied to shear and
dielectric data from the literature.
