Same with a fresh debian 9.6: Clicking 'Unlock' does nothing, console shows:
(gnome-control-center:11030): Gtk-WARNING **: Error acquiring permission: Failed to acquire permission for action-id org.gnome.controlcenter.datetime.configure ii policykit-1 0.105-18+deb9u1 i386 ii policykit-1-gnome 0.105-6 i386 Let us know if you need more info.
