Timelines are important in keeping your events consistent. When your characters meet, when they interact, when they are born, and when they die. Timelines keep things in order. Nothing aggravates your reader more than mixing up time and events.
All worlds rest on the Main Timeline no matter which universe or reality they live in. This is done so there is a point of reference of where each world exists in time relative to the other world. If you want to create a character that can travel between one or more worlds, you’ll have a reference point from where you can start.
Each world / reality will have its own timeline, so you are able to break everything down within the world itself. Timelines will contain births, deaths, construction time of building, major events, such as war, depression, recessions, murders, and more. Timelines will also reflect members stories if they wish to add them, and events that happen within the game once they are up and running.