  We study waiting times of Gamma-ray flares of Flat Spectrum Radio Quasars. We
adopt here a Scan-Statistic driven clustering method iSRS, (Pacciani 2018) to
recognize flaring states within the FERMI-LAT archival data. We found that
flares waiting times can be described with overlapping bursts of flares, with
an average burst duration of ~0.6 year, and with an average burst rate of
~1.3/y. We also found evidence for a second population of waiting times for
times shorter than several days (blue component). We found a few tens of cases
of short waiting times. In our analysis, CTA 102 showed the large majority of
short waiting times. Interestingly, the period of conspicuous detection of the
blue component of waiting times for CTA 102 coincides with the crossing time of
the K1 feature with the C1 stationary feature in radio reported in (Jorstad
2017,Casadio 2019).
  We interpret the obtained distribution of waiting times of Gamma-ray flares
as originating from cold plasma moving along the jet for a deprojected length
of ~30-60 pc (assuming a bulk Gamma=10), that sporadically produce Gamma-ray
flares. Duration and Burst rate is in agreement with distribution of fading
time and ejection rate of traveling structures observed with VLBA at 43 GHz.
