I was there in the 17th. Got to the gates at 6:30am. There were only 2 other people there. They only opened about 5 minutes early. Maybe even less than that. Managed to be on the first train on gringotts.
I'm staying at Cabana Bay and got a phone message on in-room phone sayng that early entry started at 7:00 am tomorrow and buses started running at 6:15 am.