to further what
@nickys said above....the steps in order:
1) You and your party scan your band and enter Disney Hollywood Studios .... to be safe, be inside the Park before 7:30
2) Open app....you'll see this screen 1st
3) Click Find Out More
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You see this screen next....click Join Boarding Group
By the way, at 7:53 this A.M. there are still back Groups available
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Next screen....click on everyone in your party that you want in your Boarding Group. Your Boarding Group will be constructed from your Family and Friends list, so make sure you have added everyone to your Family and Friends!
You'll get this next:
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Then you'll get this...and you've succeeded in joining/building your Boarding Group! Our group was created at 7:32 A.M. and wasn't called until 7:41 P.M.....you'll see more below
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Finally you receive this, prompting you to head over to the ride....you'll notice our group wasn't called until 7:41 P.M., and we were given to 9:41 P.M. to make it over to the ride que (9:41 is 41 mins AFTER Park Closing)
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Once you make over to the Que, you'll scan once where all the CM "Guards" are making sure no one gets in without a BG. This is a holding area just outside the ride; I assume this is for those people who have arrived and are waiting for the rest of their Boarding Group. Then you'll scan again as you enter the actual line....once you've gotten in line, the line moves very swiftly, almost so swift you'll slow down just to absorb the line que....it is pretty cool!