Evolution of CG mean surface brightness, split by CG identification redshift. Histograms of threshold times are shown in the top panels. From left to right, we show CGs identified at redshift z = 0.06, z = 0.14, and z = 0.23. The median of each is shown as a solid coloured line (dark red, magenta, and green, respectively). The vertical dotted black line indicates the identification time of each sample. CGs at different epochs evolve similarly: most cross the surface brightness threshold less than 1 Gyr before identification, reach maximum compactness shortly after, and then galaxies begin to orbit within the group. Post-identification evolution is highly diverse, reflecting the chaotic nature of these systems.