DrawingArea in Glade and somehow tie what I get from get_widget
to my instance of the Clock class?
Your new best friend: get_widget_derived [1].
Apologies if those docs are out of date but its exactly what you need. In glade, just put a DrawingArea where you want it. In code, derive from DrawingArea, add the constructor form the link talks about, and use get_widget_derived to (essentially) cast the drawingarea in glade to your derived drawing area.