Thank you, Marianne! Great questions! From what I understand, when it comes to states, the states names aren't automatically added in the alt text. But as I was researching a little more on this topic, I realized I incorrectly explained that custom message text on the first slide. Screen readers can read the text when it changes if you select the accessibility checkbox for the new text within that added state and edit the Alt Text. Here's a video example by Maria that shows what that looks like (using shapes and editing the ALT text):
https://360.articulate.com/review/content/b46673ef-b554-4f9c-9999-971c9f3d9696/reviewAs for using States for color changes, those are just visual enhancements, and the change of color is not recognized by a screen reader so don’t rely on color alone to convey meaning (whether on a state or a slide/layer).
As for the timeline, it’s a good idea to not have items appear and disappear because items can disappear before screen readers can read.