The whole competition itself had both the S and the D classes taking their respective tests at the same time, but not in the same place. From there, it would change to A class and C class, before finishing with B class.
The test itself would span across the entire school day. It wasn't exactly a free day, but you mostly just watched other people for most of the day, which was a nice thing. The teachers organized everything, getting the people paired up together amongst each other before sending them all to different places where their test would be held. For those who enjoy watching, they would have to choose who they wanted to watch, considering that all the tests were happening at once.
Though usually, people would just choose others who were part of their group.