"Rope Dropping" is when a park lets you into the first part, where the gift shops are, but then ropes off access to the rest of the park until the official opening time, when the rope "drops" and everyone can run to the first ride. The rope doesn't actually drop because people would trip over it. They move it to the side.
At IOA, they don't have a rope. They let people in at 08:45am, and when you get to the bridge leading to Hulk, a person is standing there. They have magical powers to hold hundreds of people behind the bridge until 9am.
Be at the gate at 08:30am. A line forms going past the ticket booth. You wanna be first thru the turnstyles so you can be first in line at the bridge. And sometimes they open at 08:30am, but it's never offically announced.