In the first flashback, when the twins are sneaking onto Mr. Longfellow's property, the year is 1953. However, Roderick and Madeline were born in 1950, which is revealed later in the series. They were certainly older than three years old in the flashback.
On New Year's Eve, 1979, Roderick offhandedly asks Madeline if Ronald Reagan will run for president. However, he had already announced on November 13, 1979.
Saint Teresa of Calcutta did not publicly share the quote: "Pain and suffering are like the kiss of Jesus. It just means you've come so close to him that he can kiss you" until she delivered the commencement address to the graduating class of St. Thomas Aquinas University in 1982.
Although set in the 1960s, Madeline's bra, the outline of which is visible under her rain-soaked shirt, is a style that has existed only since the mid 1970s.
The haircut of young Roderick Usher - a mop-top - would not have been appropriate in 1962 in the United States. It was made popular by the Beatles around that time in the UK, but wouldn't reach the United States until later.