The chronological timeline of the Metal Gear universe is fairly massive, more than one might expect, beginning during the first half of the 20th century and bleeding into our modern time. Out of the numerous events that occur throughout the games, many of them are given a date(and sometimes even a time) where they take place. So I thought it'd be fun to lay out all these events in order of when in the year they happened, rather than chronologically. Hence why I'm calling this page a calendar!
More entries to the calendar will be added if/when I find more instances of specific dates being given for events. The layout may also change, I would like to provide screenshots of when these dates are shown in-game.

February February 25th, 2005- Kazuhira Miller is murdered in his home by an unknown assailant(Who is implied by the post-credits scene in MGSV to be Revolver Ocelot).
February 28th, 2005- The Shadow Moses Incident.(Since the game plays out over the course of one night, you could say the incident ends on March 1st, 2005)
March March 11th, 1984- Dhekelia SBA Memorial Hospital is attacked by XOF and Venom Snake makes his escape from where he'd spent his nine year coma. This kickstarts the events of Metal Gear Solid V: The Phantom Pain.
On the same day, also in 1984, Kazuhira Miller is taken to the Soviet outpost Da Ghwandai Khar in Afghanistan by XOF's Parasite Unit.
March 16th, 1975- MSF's Mother Base is attacked by Cipher, destroying it and sending both Big Boss and MSF's medic into a coma that would last nine years.
March 21st, 1984- Kazuhira Miller is rescued by Venom Snake from Da Ghwandai Khar in Afghanistan where he had been interrogated for the past ten days.
April April 29th, 2009- The Big Shell Incident begins, with FOXHOUND rookie Raiden infiltrating the oil cleanup facility.
April 30th, 2007- Jack(later known as Raiden) meets Rosemary.
April 30th, 2009- The Big Shell Incident, and Raidens mission, ends.
June June 6th, 1944- Revolver Ocelot is born during the invasion of Normandy, his mother being The Boss, who gave birth on the battlefield. Happy birthday, Ocelot!(...I don't know if i should be that cheery about it)
August August 7th, 2007- The Tanker Incident
August 24th, 1964- The Virtuous Mission
August 30th, 1964- Operation Snake Eater commences.
September September 2nd, 1964- The Boss dies at the hands of Naked Snake, ending Operation Snake Eater and ruling it as a success for the U.S.
November November 4th, 1974- Big Boss and Kazuhira Miller are approached by Ramón Gálvez Mena and Paz Ortega Andrade who asks for MSF's help to defend their country of Costa Rica. Thus starting the events of Metal Gear Solid: Peace Walker.
December December 24th, 1999- The Zanzibar Land Disturbance.