JAM SESSION: Note to celebrities: Traffic sucks during Milan Fashion Week — especially on a rainy Friday night. January Jones arrived more than 45 minutes late to the second Versace show, and was visibly flustered. Was she stuck? “Yeah, for like an hour,” she sighed. The “Mad Men” star jetted in from London, where she is filming the next “X-Men” installment in which she plays mutant Emma Frost, whose powers include the ability to turn into a flawless diamond form. She said her next movie, “Unknown White Male,” comes out in January, and she also stars opposite Nicolas Cage in “The Hungry Rabbit Jumps.” Jones confessed she ditches the hourglass dresses when not playing Betty Draper on the “Mad Men” set, but she was pleased that the award-winning TV show has influenced designers. “It’s just given back a very feminine silhouette that’s been lacking in the past few years, bringing back the more curvy, feminine, voluptuous look,” she said.