I recommend calling Universal to see what their potential plans are in terms of opening the attraction if it's going to continue to not open until 9am, or if they do attempt to open it with the rest of the Harry Potter attractions.
I would say that regardless of whether it does, or not, there will be plenty of people that will be waiting way prior to EE to get into IoA and in order to line up for Hagrid's, so if you do not get there very early before EE in order to be one of the first few to get onto Hagrid's you might as well wait later in the afternoon, because whether they open it with EE, or wait until 9am, there is going to be plenty of people ahead of you that had been waiting if you decide to slip into the back of the line when it first opens.