The "time" in Quentin Tarantino's 2019 film Once Upon a Time... In Hollywood is 1969. The director describes that seminal year as "the height of hippie Hollywood." It was also the year of the notorious murders committed by Charles Manson's Family, which play a part in the plot, and other historical events. Many of the characters in the movie, which debuted at the 2019 Cannes Film Festival, are real people who had ties to the Manson story or Hollywood, although the main characters played by Leonardo DiCaprio and Brad Pitt (a former TV western actor and his stunt-double friend, respectively) are fictional.
Perhaps it's the magic and talent of movie makeup artists, costume designers, and hair stylists, but the casting crew did a stellar job finding actors who have an uncanny resemblance to their 1960s real-life counterparts, including Margot Robbie as Sharon Tate, Dakota Fanning as Lynette "Squeaky" Fromme, Damon Herriman as Charles Manson, and Mike Moh as Bruce Lee. You might do a double take looking at the actors as seen in the film when compared to their historical 1970s Hollywood film equivalents.