The solution
I decided to narrow it all down to one main function and design the app as a one-way journey to the final destination: the therapy day.
From the moment in which the patient finishes their onboarding, the 3 key-dates of preparation for the therapy day, are added in the calendar and become the actual menu in the form of a tab bar / timeline.
The user journey ends on the therapy day and, once this is reached, the interface and functionality of the app shifts from being a guide to being a companion. The look, feel and content must now serve the new purpose of keeping the patient company during the hours of therapy and provide useful information and knowledge articles.