You were the mom in the story huh?I forget the exact wording of the announcements, but I'm positive they don't make any sort of reference to only being available for "seconds". There is no official Disney communication that I am aware of that goes beyond the phrase "very popular". Unless you know from personal experience, research, or had a cast member explicitly tell you... how would you naturally interpret "boarding groups are open starting at 10am"?
If I'm a normal human being and not Disney obsessed, I would probably check the park hours.. see "oh, they open at 10... ok cool, as long as I get in there pretty soon after that I should be good!"... Not that the gates have been open for an hour and 5000 people are already inside fighting over 3000 slots. Even if I was in the park, had the app already downloaded and signed in, and was aware of the time... how would I possibly know I need to be sitting directly on an app page with 8 seconds leeway to act with specific intent on a button I've never seen before that moment at 10am exactly? This is a major modern ride in a currently capacity limited park! Just knowing that alone, I would be incredulous if a CM told me that I was way too late at 10:05am, 5 minutes after official park opening. The headliner rides at the other parks don't work like that at all!
As an interesting aside, I have some friends that are local APs and Star Wars fans and had been in March to the studios for their first time just before the shutdown. They loved the Falcon and loved walking around the whole land. I asked them about Rise... They had absolutely no idea it even existed. They had never downloaded the app. Walked passed the entrance area thinking it was a meet and greet line or something. Had no clue.