It really depends... If it's fresh mud, I keep it on there as long as it will stay... Mud is, after all, better than the 4 tons of salt it would otherwise accumulate on these Michigan roads... If, however, the mud has washed off to a point where it's nothing more than road dust and film, I wash and wax it...
Whatever the case, even if mudding or up north, the interior is always shampooed, armouralled, and generally spotless...