Wise Clock 3 board plugs into both connectors of the display. To cascade a second display, you will need to solder, on the Wise Clock 3 board, a right-angle 16-pin (8x2) male header in the place provided below the existing connector, then use the 16-wire ribbon cable coming with the 3216 display to connect this newly added header to the input connector of the second 3216 display, as shown in the photo below.
A demo (put together by Tim Gilmore) of a 64x16 windows sign display powered by Wise Clock 3 is shown in action in the following video. The demo software can be downloaded from here (for more details see this thread in the arduino forum).
Besides saving more, making your own clock brings a great sense of accomplishment.