I asked the admissions department about what I should include in an application update, as I started some new volunteer activities that were not reflected in my primary application. If I understand them correctly, if there is something significant you have been taking part in that isn't reflected in either your primary or secondary applications, then you should absolutely submit an academic/application update.
What they do not want to see is any sort of intent address. They specifically stated towards the end of my interview that they understand your intent through your application to the school. I would also personally try to submit the update as soon as possible, unless you have anything happening from now until 1/22 that you would like to include in such an update.