Summary of the minimal variability time scales derived from the GeV data (in grey, Vovk & Neronov 2013) and TeV data (in green, this work). The arrows indicate the variability estimates for the specific sources from Table 1. The black hole light-crossing times t_lc are shown by the solid blue (a = 0) and red (a = R_g) lines. The last stable orbit periods for the a = 0 and a = R_g cases are indicated by the blue and red dashed lines, respectively.