For satellite dwarf galaxies that were preprocessed in a group before falling into the MW/M31 halo, the maximum host-halo mass experienced during preprocessing (top) and the total duration of preprocessing (bottom), as a function of satellite stellar mass, M_star, or subhalo peak mass, ﹩{M}_{\mathrm{peak}}﹩. Solid curves shows median, shaded regions show 68%, 95%, and 99.7% of the distribution. Most preprocessing occurred in groups with ﹩{M}_{\mathrm{vir}}={10}^{10-12}\;\;{M}_{\odot }﹩, masses at which environmental effects are feasible, though poorly understood. The typical group preprocessing duration was 0.5–3.5 Gyr, though some satellites at ﹩{M}_{\mathrm{star}}\lt {10}^{7}\;\;{M}_{\odot }﹩ experienced significantly longer durations.