Maybe consider the ThemeKey module? From its project page (bold markup added here):
... allows you to define simple or sophisticated theme-switching rules which allow automatic selection of a theme depending on current path, taxonomy terms, language, node-type, and many, many other properties.
In combination with Drupal's theme inheritance you can easily achieve features like:
- a date/time-selected Christmas theme
- ...
So by using like 1 theme variation for each quarter you could get the job done, no?