Time moves slowly on the “The Americans.”

Exec producer Joel Fields said Saturday during the Television Critics Association press tour that the writing staff has been surprised at how long it’s taken to move through the early 1980s. The FX period drama revolves around covert Soviet spies played by Keri Russell and Matthew Rhys.

Fields was pressed as to whether he and exec producer/creator Joe Weisberg have an end date for the series in mind — in terms of the number of season on FX and the chronological year in the storyline. In the past the pair have hinted that the fall of the Berlin Wall in 1989 would be a logical end point for the story rooted in the last gasp of the Cold War.

The upcoming fourth season, which bows March 16, returns with the storyline picking up in 1983. Using the three-act drama metaphor, Fields said he feels like the show is “coming to the end of its second act” at the close of season four. He suggested that the tale of Philip and Elizabeth Jennings might be wrapped up with a fifth or sixth season, but he also stressed that there was no concrete decision on the span of the series. Moreover, there’s no certainty about renewals from FX.

“We’ll do what’s right for the storytelling,” Fields said. “We often surprise ourselves on how hard it is to make progress” through chronological time in the show. In season four, big historical moments that will be incorporated include the November 1983 airing of the landmark ABC TV movie “The Day After,” a dystopian look at the fallout after a nuclear attack in the U.S. by the Soviet Union. Fields rewatched the movie, directed by Nicholas Meyer and starring JoBeth Williams and Jason Robards, in preparation.

“It really holds up,” Fields said. Another media event from that year, David Copperfield’s CBS special in which he made the Statue of Liberty purportedly disappear, will also make an appearance.

In terms of the chronological end date, Fields told Variety that information was highly classified.

“We’re still exploring how that answer would play out,” Fields said. “We have some big ideas — one big idea in particular — and we’ll see if we get to that end point and if we can make it work. We thinking it would be really satisfying. We’ll see.”

Russell and Rhys talked about how the danger is heightened for their characters this season as important aspects of their cover have been blown. The Jennings’ teenage daughter Paige, now knows her parents true identity which complicates the relationship on multiple levels.

“The game has shifted in terms of parenting Paige,” Rhys said. The family in this season is focused on survival.

Holly Taylor, the actress who plays Paige, said she had high hopes for joining the family business immediately after the disclosure, but no such luck.

“I was always hoping that if Paige found out, she’d be put in a wig straight away,” Taylor joked.

Elizabeth Wagmeister contributed to this report.