You could try installing the “Split clock for vertical panels” Plasma widget and use that in the vertical toolbar:
To add it , just right-click on the vertical panel and select “Add or Manage Widgets”.
Then hit the “Get New” → “Download New Plasma Widgets” button and search for “split clock” (or just “clock” to see all available clocks). When you see the Split Clock in the list, hit the “Install” button.
After that is done, exit the desktop’s “Edit Mode”, right-click on the vertical panel again, select “Add or Manage Widgets”, and the Split Clock should now be in your list of available widgets. Click on it to add it to the panel.
Then exit from “Edit Mode” again to bring you back to your normal desktop.