if you install gnome-control-center package (e.g. because you want to use date and time settings or sound settings etc ...)
then you get a set of launchers added to /usr/share/applications/ that should launch gnome-control-center itself or the individual settings applets (e.g. sound, datetime, bluetooth etc ...)
However they don't work.
But if you drag and drop them onto you desktop or a panel you can edit the launcher: right click > properties > edit
and in the command section prefix the command with 'gksu' (e.g. gksu gnome-control-center )
also you can open /usr/share/applications/ as the administrator and edit the launchers there.
Thus it's easy to add a change time launcher to open the gnome time settings applet (command: gksu gnome-control-center datetime ) next to the xfce dateTime panel applet