Evolutionary sequence of the ALMA-IMF protoclusters, assuming that free-free emission increases over time. The 1.3 mm-to-3 mm flux ratios decrease when the free-free emission dominates the thermal dust emission at 3 mm. The provisional evolutionary stage of IR-quiet and IR-bright protoclusters is indicated by filled and empty square markers, respectively. Their revised evolutionary stage, from Young, to Intermediate, to Evolved, are shown by green, orange, and red markers, respectively.