Solution
One of elements had a height that was 200vh. Prior to my using this amazing library, it made sense to work the effects I was after. So, to ensure the scroll duration aligns with the elements in the intro, make sure the heights don't include extra space if that's not intended (obvious :)).
Summary
Conceptually, to align the end +=SomeDistance with the intro elements, greensock does that for you "auto-magically":
setting the height to the sum of the elements in the intro
setting bottom padding value to the +=SomeAmountpx
... the computed height value depends on the height of each element.
