Per (PeteCresswell):
Instead of "1", "2", and so-forth along the X axis, I want "1-7
Days", "8-30 Days", and so-forth.

I think I've got this one:

"Category (X) Axis Labels"....

Chart Props | Source Data | Series | Category (X) Axis Labels |
(Select range in source data)


Now, I guess I'm looking for something like "Category (Y) Axis
Labels" - but it isn't 100% analogous bc now I'm looking to label
the tick marks instead of associating labels with values in the
series.
--
PeteCresswell