  Quantum kicked rotor was recently realized in experiments with cold atomic
gases and standing optical waves. As predicted, it exhibits dynamical
localization in the momentum space. Here we consider the weak localization
regime concentrating on the Ehrenfest time scale. The later accounts for the
spread-time of a minimal wavepacket and is proportional to the logarithm of the
Planck constant. We show that the onset of the dynamical localization is
essentially delayed by four Ehrenfest times and give quantitative predictions
suitable for an experimental verification.
