We view the 1920s as completely different from the 1960s, and the 1970s as completely different from today. How did this work in say, the 16th century? Was the 1660s seen as completely different time from those in 1680? Or were things fairly stagnant up until the 20th century?
Yes, and the degree of change was different in different places. There were fairly frequent wars, civil wars and other upheavals which hugely changed society and culture. Technology changes tended to be broader scale, such as the agricultural revolution and the industrial revolution, but one could argue that the 19th century saw more social, cultural and technological change than the 20th in many ways.