I always recommend getting to Halloween Horror Nights early, but that advice is becoming more essential as the season moves into October.
Even though the event starts in September, many people don't get into the spirit until the calendar moves on. Now that it's October, the crowds are noticeably growing and the haunted house wait times are on the upswing. I watched them rise past an hour on the first Friday in October as the night wore on and more and more people flooded the park. Expect the crowd to stay high, as years with popular intellectual properties like The Walking Dead and Evil Dead always draw them in.
So how does early arrival help you? Does it make a different even on the most crowded nights? Here's my take on the topic, based on going to the event almost every night:
1) Getting there early is especially helpful on week nights when most people are at school or at work. Later in the season, the schools will have some off time and the crowds will build faster. However, for the past two weeks I've enjoyed the nearly deserted early Thursdays. Fridays are less crowded early, too, but not to as great of an extent. I suspect many people ditch work early on the final day of the week.
2) Early arrival is still helpful, even on the weekend. People tend to move slow. It's human nature. There's always a flock of early birds, but they're nothing compared to the crowds that roll out after dinner. Use that human nature to your advantage, both in getting to Halloween Horror Nights before opening time and it going against the typical traffic flow. Go right while everyone else walks straight down the main path to the sounds stage houses and you'll practically walk right into Walking Dead and La Llorona. Go to Havoc next because Afterlife doesn't open until 6:30.
3) Early arrival helps with more than just the haunted house lines. Not only do the haunted house lines get long later in the evening, but so does the line to get into the parking garage. Then you're caught in a conga line of confused cars inching to the actual parking spaces in the garage. Next is the bag check, then metal detectors, then the actual wait to get into the park. You eliminate most of that if you get to the park before the event opens (or have a day ticket and stay in one of the waiting areas inside).
Those are the three biggest reasons I always arrive before opening time. Crowds are inevitable, but that early quiet time is priceless, so use it to your advantage.