Rope Drop is a way to spread out guest before the park opens.
If it's a low traffic day or a morning magic day people just go in when the clock strikes 9am in your case.
If it is a busy day they will let people in about 10 minutes before (9 in your case) to the end of main street stopping people where the road opens up to the hub. At 9 they will let these people procede further into the park.
In either case the official opening is 9 though in the second you can shop and get food on main street early.