Finite Line

The Finite Line is the first line of defense for the Southern Timeline, set up by the Ticketmaster to prevent the IAEA from crossing timelines. It forbids all transit between the North and the South timeline except for a small 2 and a half minute window at 2:30am. There are only specific points one can cross the Finite Line, and most of them are through Dimensional Doors.

Dimensional Doors
Dimensional Doors are doors are locked until the 2 and a half minute window where the Finite Line is weak. These doors are tall, usually wooden, and seemingly indestructible. When a user crosses through one, they can stay in the other timeline until 2:32am when the doors close.Then they are banished back to their own timeline until the door opens again.

Other Methods of Crossing the Finite Line
Specially modified vehicles can also cross the Finite Line. Such vehicles are still limited to crossing within the 2 minute time frame. However, once the time frame is over at 2:32am, the passenger will still be able to stay in the timeline they have just traveled to.