My guess is February 20, as the 13th is the Grammy Awards. That way, we'll be looking at a May 15 finale due to a pre-emption for the ACM Awards. However, look for a 2-hour episode sometime this season so that it can end on Mother's Day again (that's the only reason why TPTB would give us a 2-hour show).
That, and they need to get Survivor in (though it could still air a week later and still avoid the Memorial Day holiday). Whatever happens, my money is on 2/20/2011 but it [TAR18] won't be before the Super Bowl unless they can rebound from a two-week break.