The dconf-editor program provides a graphical interface for editing settings that are stored in the dconf database. The gsettings(1) utility provides similar functionality on the commandline.
So install this package if it is not available. Let's launch the app.
dconf-editor window popup. On the left tree menu, expand in this succession. org -> gnome -> desktop -> interface . Check the button for the field you would like to enable. In the screenshot below, I have enable my use to desktop setting, show the date and show seconds.
That's it, in the next article, we will probably look into the earth daylight map on the date / time calendar. I like that feature too but somehow it is not available in gnome3.