The decay of autoionizing electronic wave packets of rubidium in a static electric field of 2.0 kV/cm is studied. Using an atomic streak camera, the escape of the laser-excited Rydberg wave packets over the saddle point is measured. New information on the ionization dynamics is obtained that cannot be retrieved from optical recurrence spectra. For laser excitation perpendicular to the electric field at scaled energy e = - 1.74, the main ionization is delayed by 12 ps. For parallel polarization (e = - 1.32) the ionization occurs in two bursts, 7 ps separated.