Thanks to all for sharing your experiences! Just returned home and successfully rode RotR 3 times (last ride today required a bit of help from CMs).
Day 1: Arrived before park opening (6 am), inside park by 5:35 am, got BG 20 right at 6 am, Group called at 6:30 am
Day 2: Tapped into park at 6:01 (park opened at 6 am), received BG 101 at 6:02, Group called ~1:00 pm
Day 3 (this morning): Tapped into park at 6:33 am (7 am park opening), but at 7 am the Join Boarding Group button would not go live on either phone - one was on WDW WiFi, one on ATT, one start fresh starting the app right at 7 while the other was already in the app and kept refreshing. Neither phone would even allow us to get a BG until 7:04 and got 128. We were not the only guests with this issue this morning and folks around us had the same problem. Problem was, our flight home left at 1:30 pm and we knew from previous days (and this thread) that would never be called in time. After sharing our circumstances with a CM, we were allowed to tap in early so we could ride before having to leave today. Of course, I then had to drive lightspeed to make it to the airport in time!