Interregnum

Modern period, zeitgeist, i.e. Modernity, starts ca 1600 or more precisely begins at the fall of Constantinople in 1453 which signalled the end of the Middle-Ages and of an era (Constantinople was the capital of the Eastern Roman Empire, aka Byzantium). a few decades later Luther nailed his thesis on his local Romish Church's door, another nail in the dying body of the Middle-Ages. Gutenberg started his movable type for printing circa around the end of Byzantium, and mass printing techniques were essential to the forming of the Modern mind (which is connected to quantity: i.e. math, mass production and mass culture). the Renaissance had happened not long before, and started a new wave of a proto-scientific mindset. Francis Bacon then adds another nail around 1600. Newton not long after that. and by the Enlightenment so-called, (1715) we're pretty much done. 1760 and you're in Central Modernity—the Industrial Revolution starts. By the 1950s you're already in Late Modernity—the Soviet Union was on of the biggest end points of Modernity, and by 1990 you're already in High Postmodernity.
Postmodernity then starts arguably with Nietzsche, in 1873 with his «On Truth and Lies in a Nonmoral Sense» (which in 2004 ca changed my brain). Nietzsche said that we'd have 200 years of Nihilism, which is more right than ever now (2018). Nietzsche said in ca 1887 we would have 200 years of Nihilism, but Nihilism is pretty much what people popularly call Postmodernism—i.e. extreme relativism, etc. so according to that "Postmodernism" (Nihilism) will be dead by 2087.
We're approaching Late Postmodernity by now, in the year of our Lord, 2018 AD.