Model Requirements and MVC Conceptual Designs.
On Wednesday morning you'll flesh out the functional requirements model of your system along with developing a detailed set of behavior requirements in the form of a detailed use case model with each use case defined in terms of its Models, Views, and Controllers. These behavior models will consider all of the rainy-day scenarios, corner cases, and edge cases that you got to skip when you were prototyping. All of this modeling work is done in parallel so you'll get a lot done in a day.
On Wednesday afternoon you'll update the domain model to reflect the feedback gained from the prototyping, and re-generate the database, API, and API docs.