Devil Survivor has a branching encounter system that uses events from earlier portions of the game to determine the options available later in the game. For this reason, times listed for particular events can vary from one play-through to the next, and some events may not be available at all depending on whether or not prerequisites for the event have been met. Wherever possible such prerequisites will be listed. Generally, if a particular character is listed at a second or third location at a later time, it will require the main character to have already gone through an event with that character at the earlier time(s).
Most of the events offer a couple of choices for the player to make which may affect the main character's relationship with the character, or help define the main character's worldview. Otherwise, the events help further the storyline and usually determine how a particular story arc will continue in the game.