The Metal Gear Solid V games fall immediately after the events of Peace Walker in the Metal Gear timeline. The first part, Ground Zeroes, happens immediately after Peace Walker in 1974 in similar fashion to the Tanker section of Metal Gear Solid 2. Afterwards, John/Naked Snake/Big Boss is in a coma for 9 years which then opens up as The Phantom Pain (1983). It comes 11 years before the events of the original Metal Gear (1995).
Metal Gear Solid V will show the transformation of Big Boss the protagonist from today's games to Big Boss the antagonist on NES.