Timeline and possible scenario SBM
Ollipop, great timeline! And I think your timeline is very plausible.
As to whether the girls could make it to that point, here's my possible scenario:
Elizabeth and Lyric both know they are supposed to stay within a block or so of Elizabeth's house. Individually, each of them would probably do so. But when you put two kids together, it's normal for them to sometimes egg each other on into a little mischief. The weather has cooled down from the horrid highs earlier in the week and they're feeling frisky.
They decide to ride from in front of their house around the loop of Meyer's Lake and back without grandma knowing. They're eight and ten years old and it's a thrill to think of going that far without getting into trouble.
So they start racing down to Meyer's Lake, pedalling their little hearts out. They may even have decided to make it a race. In any case, they're all hyped up because they know that they are doing something they shouldn't do.
The thrills of childhood!
And then, something goes wrong at Meyer's lake, very very wrong.
I think your theory, Ollipop, is correct.