Do you have a second day as a backup? If so, I would wait until later into the early afternoon. It typically slows down after the initial rush. After dark is also really cool, and you can get in line right before park closing.
But, if you have just the one day, you might want to plan to be at the park during the early opening hour and wait at the barricade as early as you'd like to be at the front of the non-early entry rush.