Time is the most important part of keeping a movie’s budget under control; every day of production is another day you have to pay the crew. “Oppenheimer” was originally supposed to take 85 days to film, but Nolan reorganized the whole production schedule and managed to “cut it down by at least 30 days,” according to Variety. The shorter schedule meant he had more spending money to “reconstruct Los Alamos from scratch in New Mexico,” as well as film at Berkley for the scenes where Oppenheimer lived and worked there.
The film’s executive producer Tom Hayslip was originally resistant to letting Nolan both build a fake town and film all over the country. “We want to shoot in New York and New Jersey and Berkeley and Los Angeles and New Mexico,” production designer Ruth De Jong recalled, which was considered a tall order. But then Hayslip changed his tune once he saw the sheer amount of days Nolan had cut from the production schedule.
“That is a lot of money we get back!” De Jong explained. “At that point, you feel like, ‘I have to deliver above and beyond because he just went and gave up his days.'” Sure enough, Nolan received most of what he asked for, with the only real concession being that he couldn’t film on location in Washington D.C. “Nolan was not permitted to shoot in actual government buildings in D.C.,” per Variety, so he had to film those scenes in New Mexico instead. In the end, “Oppenheimer” wasn’t just finished within budget and ahead of schedule; it was within budget largely because it was ahead of schedule.