*BIG SPOILERS! READ AT YOUR OWN RISK!*
The year of John's birth, who will be known as Naked Snake years after.
The year of Huey Emmerich's birth.
The year when the events of Metal Gear Solid 3: Snake Eater take place, starting with the Virtuous Mission then going through the Operation Snake Eater and ending with Naked Snake killing his mentor, The Boss. He will become Big Boss.
After disagreeing with Zero's ambitions, Big Boss forms the mercenary company, "Militaires Sans Frontieres", with Kazuhira "Kaz" Miller, a mercenary that he met during a mission. They will build the Mother Base together.
The date when the events of Metal Gear Solid: Peace Walker take place. During his adventure, Big Boss will meet Chico and Paz.
The date when the events of Metal Gear Solid V: Ground Zeroes take place.
So start the events of Metal Gear Solid V: The Phantom Pain...