  Attosecond dynamics of electron reflection from a thin film is studied based
on a one-dimensional jellium model. Following the Eisenbud-Wigner-Smith
concept, the reflection time delay $\Delta\tau_{\rm R}$ is calculated as the
energy derivative of the phase of the complex reflection amplitude $r$. For a
purely elastic scattering by a jellium slab of a finite thickness $d$ the
transmission probability $T$ oscillates with the momentum $K$ in the solid with
a period $\pi/d$, and $\Delta\tau_{\rm R}$ closely follows these oscillations.
The reflection delay averaged over an energy interval grows with $d$, but in
the limit of $d\to\infty$ the amplitude $r$ becomes real, so $\Delta\tau_{\rm
R}$ vanishes. This picture changes substantially with the inclusion of an
absorbing potential $-iV_{\rm i}$: As expected, for a sufficiently thick slab
the reflection amplitude now tends to its asymptotic value for a semi-infinite
crystal. Interestingly, for $V_{\rm i} \ne 0$, around the $T(E)$ maxima, the
$\Delta\tau_{\rm R}(E)$ curve strongly deviates from $T(E)$, showing a narrow
dip just at the $\Delta\tau_{\rm R}(E)$ maximum for $V_{\rm i}=0$. An
analytical theory of this counterintuitive behavior is developed.
