1:23:45

Series director Johan Renck was in charge of directing the episode.

Screenwriter Craig Mazin was recognized for primarily working in comedies for the last 20 years such as Scary Movie, Identity Thief, and The Hangover. Mazin considered working on Chernobyl easier than comedies, "It’s brutal. It requires a sense of logic, and it requires a kind of intellectual capacity. Some of the smartest people I know are comedy writers. You have to be transgressive, but you also have to understand character. When I was writing Chernobyl, it seemed very natural to me."[2][3] In order to capture the show's full scope of the explosion, Mazin went to the Chernobyl Exclusion Zone, stating: "That required kind of both living inside that mind in that culture and sharing the scripts early on with people who grew up in Soviet Ukraine and having them vet through things. Insane attention to tiny details, clothing, watches, glasses, everything. Shooting in Lithuania, a lot of our crew were old enough to remember what it was like living in the Soviet Union. They would let us know, ‘You know, if you brought your lunch to work, you would use a briefcase for that. You wouldn’t use a paper bag."[4]

In 2014, Mazin developed an interest in adapting the Chernobyl disaster and began researching for the project by reading books and interviewing nuclear scientists with the hopes of getting the most accurate portrayal of the explosion to the series.[5] He stated: "Well, at the heart of this story is a question about what happens when we disconnect from the truth. And the Soviet system was essentially an enormous monument to the useful lie. They made lying an art: They lied to each other, they lied to the people above them, they lied to the people below them, and they did it out of a sense of survival. Ultimately, it just became expected, and the truth was debased. When it did kind of peek its head out, it was attacked. So I thought the worst possible thing I could do in telling a story like that would be to contribute to that problem by over-fictionalizing, over-dramatizing."[6] He also revealed that he wanted to show the audience that lying, arrogance, and suppression of criticism are indeed the real danger that lead to the disaster and not nuclear power.[7]

On July 26, 2017, it was announced that Johan Renck would direct the miniseries, having previously worked on some episodes of Breaking Bad and The Walking Dead.[8] Renck expressed interest in directing the show after reading the script due to his interest on dark stories, explaining: "It basically started with a script showing up on my desk one day. The title alone interested me a lot because this kind of tragically dark, eerie and dramatic story tends to suit my taste. It’s the stuff I respond to. I’m from Sweden originally and lived in Stockholm in 1986 when the catastrophe occurred, so I remember it vividly because while Sweden wasn’t hit by it they were also the first ones to understand something had happened outside of the Soviet since they’d put a lid on it." The series horror elements due to Renck wanting to portray the disater with his "own feelings and perception of reality rather than trying to sort of work within the realm of film and have to use those traditional tools"[9]

The producers originally intended to have Daniel Day-Lewis in the lead role as Valery Legasov, but the former retired from acting just a few days before the series announcement following the completation of his last film Phantom Thread.[10] On June 26, 2017, it was confirmed that Jared Harris would be joining the series as Legasov;[11] "I felt some responsibility, but I’m not playing the historical figure. The script made some changes to the real events to focus on the story between Legasov and Shcherbina, so you need to figure out your role in the story and then use your imagination to connect with the material."[12] Instead of using a Russian accent, Harris used his natural one as the characters were ‘speaking in their own language’ and deemed that it would made better sense for the actors to use their respective accents.[13]

On March 19, 2018, it was confirmed that Stellan Skarsgård would join the series in the role of Boris Shcherbina and stated: "Nobody would see it as a privilege to spend five months in a dilapidated nuclear plant, unless it was to play in a script like this by Craig Mazin, work with a director like Johan Renck, collaborate with a producer like Jane Featherstone, jam with an actor like Jared Harris and finally be at the feet of Emily Watson whom I have been missing for some 20 years."[14] Adam Nagaitis and Jessie Buckley were cast in the series portraying Vasily Ignatenko and Lyudmilla Ignatenko respectively.[15][16] The episode also stars Paul Ritter as Anatoly Dyatlov, Con O'Neill as Viktor Bryukhanov, Adrian Rawlins as Nikolai Fomin, Sam Troughton as Aleksandr Akimov, and Robert Emms as Leonid Toptunov.[17][18]

The filming for the show began its principal photography in April 2018, in Lithuania, due to keeping the same architecture during its period of the country still being part of the Soviet Union.[19] In order to portray the city of Pripyat for the series, filming took place at the residential district of Fabijoniškės in the city of Vilnius.[20] The main reason for the crew to not film at Pripyat is due to the current deteriorating state that the city is in after its evacuation following the disaster, as it was needed to represent the city as it was during the time of the incident. Mazin also revealed that it is still dangerous to film close to Chernobyl, as 20,000 years need to pass in order to become available for human habitation again.[21][22] The scenes that took place at the power plant were filmed at the Ignalina Nuclear Power Plant, due to both of them being very similar which has been closed since 2009.[23]

The episode's title refers to the exact time of the clock when the reactor 4 of the Chernobyl nuclear plant exploded, at 1:23:45 AM on April 26, 1986.[24] It also depicts the exact time of when Legasov committed suicide in order to coincide with the second anniversary of the Chernobyl explosion. However this is only used in the episode for dramatic purposes as Legasov in reality committed suicide a day later.[25]

"1:23:45" was first released in the United States through HBO on May 6, 2019, where it was seen by 756,000 viewers.[26] It was followed by its release in the United Kingdom and Republic of Ireland through Sky Atlantic on May 7, 2019, where it obtained a total of 861,000 viewers.[27]

"1:23:45" received acclaim from critics. David Griffin from IGN commented "HBO's Chernobyl is a brilliant and emotionally draining dive into a horrific event. Stellan Skarsgård, Jared Harris, and Emily Watson give memorable performances that are amplified by Johan Renck's skillful direction and Craig Mazin's sharp writing. While the horrors of Chernobyl might be difficult to stomach, the narrative journey is worth sticking around for... Even if it causes you to squirm from time to time."[28] Ed Cumming from The Independent rated the episode with 5 stars and stated: "The threat of nuclear war may have abated but as metaphors, radiation and fallout are as powerful as they were 30 years ago. Timely, bleak, intelligent and compelling, Chernobyl is a triumph of a disaster." Adam Starkey from Metro also gave the episode 5 stars and considered that "Some might find Chernobyl too bleak to enjoy, but very few shows land with such a startling and unsettling first impression. As entertainment, a retelling of the disaster, and a warning of scarily relevant dangers, Chernobyl is a staggering, unmissable achievement which will haunt you for weeks."[29]

Lucy Mangan from The Guardian gave the episode 3 stars praising Ritter's performance and calling it "part of a uniformly excellent parade of performances fighting to make coherence out of chaos", but was critical of not showing more of the accurate effects, hoping that the show would improve in the following episodes: "With Jared Harris starring, this miniseries about the 1986 meltdown should be gripping – but instead strands viewers in a bewildering cloud of unanswered questions."[30] David Fear from the Rolling Stone rated the episode with 3.5 stars and stated that the series "spend(s) some five fours showing how a perfect storm of screw-ups and cover-ups led to a genuine catastrophe, as well as diving into an aftermath of devastation that plays like a slow-motion nightmare."[31] Sophie Gilbert from The Atlantic lauded the performances of the three lead actors "that are titans that they manage to carry of dialogue that could be cumbersome in lesser hands. While not much wears faster than bad Vladivostok burrs from RADA trained artists, the cadences here are so extremely British that cultural dissonance sometimes sets in."[32] Keith Phipps from TV Guide praised the show for its accuracies, stating, "The series details what took place before and after the reactor explosion but also the conditions that allowed it to happen, and which came close to making it even worse. As such, it doubles as a warning about who pays the cost when the hard facts of science butt up against political agendas, whether decades ago on the other side of the Iron Curtain or here and now. Some bad decisions have half-lives that last for centuries."[33]

Allison Keene from Collider rated the show with a perfect score of 5 stars and considered the show to be a "cautionary tale bigger than just the nuclear power industry, or even the environment. The cautionary tale here is about what happens when people choose to ignore the truth. It doesn’t care, as it turns out – the truth does not care. The world gets hotter whether we agree with it or not, and that is something that I hope people can take away from the show – that in the end, we have choices about what we will or will not confront as true, but the truth does not care, and it will come to pass."[34] Nick Schager from The Daily Beast stated that "Chernobyl has transformed from a story about plant-operator faults to one about systematic deception on the part of the stubborn, arrogant, blind and foolish Soviets, whose communist culture—demanding absolute loyalty to the Party, which is always perfect and infallible, even when facts say otherwise—compelled everyone to cover up the truth lest they be vilified as nation-besmirching traitors."[35]