Tower Training was a popular event inside the military. Although it had a defined schedule, once in three months, but the schedule often changed. It was because it needed to adjust to the event that happened in Gaia.
Tower Training was usually given to the unassigned soldiers. However, they allowed other soldiers who wanted to join as long as it didn't interfere with their mission. But, they still need to register first to be allowed.
When a soldier was free, he would definitely join this event. It was because the rewards were too enticing to reject. The said rewards were not things. It was a qualitative change in their body. Each soldier, who joined the Tower Training, had given testimony. They said there was a qualitative change in their body after joining the training. Hence, many soldiers had always wanted to participate in the training.