Consider "Happy Days", made in the 1970s to celebrate the 1950s. The wave of mods and paisley jangle pop in the 1980s to celebrate the 1960s. All the "Big Star" sounding bands of the late eighties and early nineties celebrating Alex Chilton circa 1972.
I would guess the movies are a lagging trend, the real number is likely 20 years, approximately equating to mid childhood, early teens as being idealised and getting expressed in successful adulthood at 30 in pop culture by those who experienced those times in formative years.
That would put the first wave of 80s nostalgia in the 2000s[0]
Stranger things is more like nostalgia for early 2000s 80s nostalgia.
Edit: the twenty year rule? [1] [2]
[0] http://www.inthe00s.com/archive/inthe00s/smf/1342451842.shtm...
[1] https://decades.medium.com/how-1980s-nostalgia-ruled-the-200...