In a year in which a three-hour-plus film, “Jeanne Dielman, 23, quai du Commerce, 1080 Bruxelles,” was named the best film of all time in the decennial Sight and Sound poll, and another three-hour movie, “Avatar: The Way of Water,” became the third-biggest box-office hit ever, it’s hard to imagine that anyone in the art or the business of movies is put off by long running times. But the announcement, in February, that Martin Scorsese’s new film, “Killers of the Flower Moon” (based on a book by the New Yorker writer David Grann), was going to be three hours plus was accompanied by a report that the Cannes Film Festival (coming in May) would be unwilling to screen it at such a length. Fortunately, the festival executives’ philistine rigidity gave way: after weeks of speculation regarding the length of the film (climbing as high as three hours and fifty-four minutes), it’s been confirmed that it will première at the festival (as of now, out of competition) at a run time of three hours and twenty-six minutes.