  We investigate the time evolution of the entropy for a paradigmatic
conservative dynamical system, the standard map, for different values of its
controlling parameter $a$. When the phase space is sufficiently ``chaotic''
(i.e., for large $|a|$), we reproduce previous results. For small values of
$|a|$, when the phase space becomes an intricate structure with the coexistence
of chaotic and regular regions, an anomalous regime emerges. We characterize
this anomalous regime with the generalized nonextensive entropy, and we observe
that for values of $a$ approaching zero, it lasts for an increasingly large
time. This scenario displays a striking analogy with recent observations made
in isolated classical long-range $N$-body Hamiltonians, where, for a large
class of initial conditions, a metastable state (whose duration diverges with
$1/N\to 0$) is observed before it crosses over to the usual, Boltzmann-Gibbs
regime.
