  The plateau in the duration distribution of long Gamma-Ray Bursts (LGRBs)
provides a direct observational evidence for the Collapsar model. The plateau
reflects the fact that the observed duration satisfies: $T_{90} = t_{e}-t_{b}$
where $t_{e}$ is the time that the central engine operates and $t_{b}$ is a
threshold time, interpreted within the Collapsar model as the time it takes for
the relativistic jet to penetrate the stellar envelope. Numerical simulation
and macronova observations suggest that compact binary mergers involve mass
ejection. If short-Gamma Ray Bursts (sGRBs) arise from such mergers, their jets
should cross this surrounding ejecta before producing the prompt emission. Like
in LGRBs, this should result in a distinct short plateau in the GRBs' duration
distribution. We present a new analysis of the duration distribution for the
three GRB satellites: BATSE, {\it Swift} and Fermi. We find a clear evidence
for a short ($\sim 0.4$ sec) plateau in the duration distribution. This plateau
is consistent with the expected jet crossing time, provided that the ejecta is
of order of a few percent of solar masses.
