We used the first day to understand all the scope. On this day, besides the people who would work on the war room, there were some other stakeholders, too. We did this because on the ideation part of the process it was very important that everybody understood the mainly possible features that we could use.
As there were already some projects using the platform we wanted to create (but each one with its particularity), we collected all the information we had to put the things together. Our job was to create a framework that could be used for every client, so we needed to know all the features to define which ones we should include at the MVP. After choosing those features, we wrote down into post-its some project assumptions that were important for us to consider. Those assumptions we glued to the wall, because they were our guide on the rest of the project.
Actually, on our "diverge" step, we didn't draw anything at all. Mainly because of lack of time, but also because we discussed those features all day long and everything was fresh on our minds.
At the end of the day, I created a simplified information architecture, that I used the next day with the team to define which tasks we were going to validate after constructing the prototype.