Is "Attack on Titan" taking place in the past or in the future?
Let’s say in my opinion, Attack on Titan takes place currently in the year 2350...

Also, "X" stands for "when Titans arrived":


Prehistory (Beginning of time until Zero Before X)
990 years Before X - the Great Titan War begins
Zero years Before X - the Titans arrived


History (Zero Before X to 835 After X)


743 Years After X (2243) - the Great Titan War ends
835 Years After X (2335) - Eren and Mikasa are born in Wall Rose


The story of Attack on Titan (835 to 854 After X)


845 Years After X (2345) - Wall Maria is invaded by the Titans
850 Years After X (2350) - Attack on Titan takes place
851 Years After X (2351) - Wall Maria is set out for the First Time
854 Years After X (2354) - The Future of Attack on Titan