"I don't care how much you love it," Robbie Fairchild groans theatrically. "Who wants to take ballet at 6:30 in the morning?"

But for a span of roughly four months, that was part of the daily routine for the dancers appearing in Cats, Tom Hooper's new film adaptation of the iconic Andrew Lloyd Webber musical, which opens in theaters December 20. The cast boasts A-list talent pulled from the worlds of acting (Dame Judi Dench, Sir Ian McKellan), music (Jennifer Hudson, Taylor Swift) and dance—most prominently, Royal Ballet principal Francesca Hayward, who makes her big-screen debut as Victoria, one of the film's leading roles. Because she was expected to get right back into company rehearsals as soon as filming concluded, there was a ballet teacher and an accompanist on set every morning so Hayward, and castmates such as Fairchild (who plays Munkustrap) and Royal Ballet principal Steven McRae (who plays Skimbleshanks), could warm up and stay in shape. With 12-hour shoot days, 6:30 am was frequently the only time available for class.