When Does "Metal Gear: Ghost Babel" (2000) Take Place?
"Metaru Gia: Gōsuto Baberu"/"Metal Gear: Ghost Babel" (released to English-speaking audiences as "Metal Gear Solid") is a spy video game written by Tomokazu Fukushima with Hideo Kojima that released April 27th, 2000. So when is "Ghost Babel" set?
It takes place on an alternate timeline of the fictional Metal Gear universe in the year:
We know this because in the very first scene, Colonel Roy Campbell tells Solid Snake about his upcoming mission and includes the phrase, ..."Metal Gear in Outer Heaven seven years ago.", referring to the final events of "Metal Gear" (1987), which take place in 1995 AD or 1996 AD.

2002 AD or 2003 AD
We know this because in the very first scene, Colonel Roy Campbell tells Solid Snake about his upcoming mission and includes the phrase, ..."Metal Gear in Outer Heaven seven years ago.", referring to the final events of "Metal Gear" (1987), which take place in 1995 AD or 1996 AD.
Much later, while interrogating someone, Solid Snake says, "seven years ago, during the Outer Heaven incident", again referring to the famous first Metal Gear game.
1995 + 7 = 2002
or
1996 + 7 = 2003.