Okay, I'm staying onsite at HRH, and have been monitoring the park wait times with the Lines app. Gringotts has the longest lines right at 8:00 am, believe it or not. We arrived yesterday about 10 AM and line times were going down, not up. Since DH did not want to leave his big camera in a locker, we decided to ride in the afternoon instead. About a 30 minute wait.
This morning, we tried to make early opening, but with sons 15 and 20, we just about made it for 8:00 AM. 7:00 AM was just too difficult. We opted for IOA and Forbidden Journey first with a <15 minute wait, folowed by Dueling Dragons with no wait. We then jumped on Hogwarts Express to US-Kings Cross Station. Since we inadvertently missed the "vanishing" effect the day before, we walked the queue as if getting back on Hogwarts to IOA, and then exited before getting on the train again. We then rode Gringotts (15 minute wait) and got Butterbeer ice cream while exploring Diagon Alley in detail while it was still mostly shady. By about 10:30 AM we headed to visit other US attractions, but that 2.5 hour immersive Harry Potter two park immersive experience was really wonderful. I highly recommend it.