This is what the D23 Expo site says. So, I think everyone is going to be in the D23 Arena line at 8:00am and you won't have to worry about the D23 Member line which doesn't open until 9:00am.
Upon arrival, there will be signs clearly visible to direct you to the entrances of the D23 Expo areas you wish to visit first:
The D23 Arena entrance will open as early as 8:00 a.m. to all attendees for the Friday and Saturday morning sessions. Since recording devices will not be allowed at select D23 Arena presentations, a camera check location will be available. Please check back here or our mobile app (available in July through the iTunes and Google Play Stores) for the most up-to-date information.