  The time dependent pion emission rate and the mean life time of the pion
source in the center of mass frame of the two-jet events have been determined
for $e^+-e^- \to hadrons$ at $\sqrt{s} = 20 - 50$ GeV by the Dynamical String
Model. It was established that the time needed for the creation of the pion
source is $5$ fm/c, whereas its life time is $\tau_0 \approx 7 - 13$ fm/c for
energies $\sqrt{s} = 20 - 50$ GeV, respectively.
