Stephen King wrote a book about this. His answer was the 1960s. The book is 11/22/63, which is the date of the John F. Kennedy assassination, as in, his main character is ultimately going back not just to prevent it, but to see if Oswald acted alone. But the way he writes about the time period tells me King really just wanted to revisit the decade of his youth. Born in 1948, King would have been 10 in 1958, the year his character travels to, and he would have been about 15 when Kennedy was assassinated. (Highly recommend the book. One of my favourites of his. And it's not horror. It's Americana, nostalgia, with a side of fantasy (the time travel bit).)

So when I say, my gut reaction is the mid-to-late 80s, to early 90s, I guess he and I have a similar idea, but King had way loftier ambitions.