Time since virial infall for satellite dwarf galaxies at z = 0 as a function of their stellar mass, M_star, or subhalo peak mass, ﹩{M}_{\mathrm{peak}}﹩: time since first crossing within R_vir of any host halo, thus including group preprocessing (left), or time since first crossing within R_vir of the MW/M31 halo (right). Curves show median, shaded regions show 68%, 95%, and 99.7% of the distribution. Satellites at z = 0 have been satellites typically for over half of their history. Lower-mass satellites fell in earlier, though with large scatter. Dotted line at z = 6 marks the end of cosmic reionization; during reionization, ﹩\lt 4\%﹩ of current satellite galaxies were a satellite in a host halo, and none were in the MW/M31 halo, demonstrating that the effects of reionization vs. host-halo environment occurred at distinct epochs, separated typically by 2–4 Gyr, and thus are separable in time theoretically and, in principle, observationally, during satellites’ evolutionary histories.