Asked and answered! The drivers fly in on Thursday for races that qualifying is on Friday. Practice will start early on Friday, thus they don't want to get up at the buttcrack of dawn to get there. In addition, they don't want to get screwed if the aircraft has a mechanical. There is a chance some of the guys could fly back out tomorrow night. This all depends on sponsor obligations or if there is another race they want to run later that night.
Looks like Michael Waltrip went into ADG. As for JXN, it looks like Dale Jarrett, Clint Bowyer, and Joe Nemechek...along with a few team planes are scheduled in over the next few hours. I see a bunch of other guys flying all over the place, but they are sure to end up at JXN or ADG before the day is up.