Some houses open at 6 and the rest at 7 (map has listings). I suggest that you get in a line for a house before 6 (probably Zombie High or Club Blood since they're next to each other, then moving down to Slaughter House and so on).
The three outdoor attractions should be done later, but keep in mind that Blueridge Bloodbath has a really long line.
I would write up a good report, but I will not be at a computer all weekend. I will say to get in line for the 6pm mazes 5-10 minutes before and then work your way around those few. After that, you will want to get in line for Blue Ridge Bloodbath a little bit before 7 if you would like the experience. The maze isn't much, but it is unique. Don't do CornStalkers until after 8:30-9. It will be walk on at that point.