Hello,
the latest sscomp time of the mminfo command for this group can give an approximate value.
mminfo -ot -q "group='your_group',savetime>1 day ago" -r "sscomp(20)"
or
mminfo -t yesterday -q "group='your_group'" -r "sscomp(20)"
But if you want a precise value the only way is the savegroup completion or the nsradmin command.