I found a Plone how-to on adding a portlet with editable text. It took a little debugging to make it work. The most important thing is to make sure the folder and document it's referring to actually exist.

I modified that portlet to create a countdown to election portlet with a small Python formula that calculates this on the fly. You have to edit the portlet itself to change the title "Election countdown" and target date. It's simple, but I'll have to figure out how to make this a parameter someday.