It's official: 24 will relocate to Mondays at 9 pm when it kicks off its fourth season in January '05. Kiefer and Co. will be paired with Athens, a college-set soap penned by O.C. creator Josh Schwartz. And as hinted Wednesday, The O.C. will shift to Thursdays in November, when it will lead into Tru Calling. Other highlights from Fox's three-tiered, year-round sked: A sketch comedy hosted by Kelsey Grammer bows in January; Arrested Development moves to 8:30 pm Sunday following The Simpsons; and Apprentice clone The Billionaire will occupy American Idol's Tuesday perch for the first half of the season. For analysis of the network's new schedules, read The Biz.