Are you leaving out more text in those tomes than what you've quoted? If so, feel free to ignore my questions to you.

Q1) I'm not sure where you're getting that anything is neutral now or that elements have both an Astral and Umbral side. Sometimes things are referred to both in single element terms and in Astral/Umbral terms at the same time, and thus, sometimes the elements' astral/umbral-ness don't line-up with the astral/umbral cycle being referred to, but I just see them as completely separate when referenced like that (such as in chapter 3).

Q2) Where are you getting 2 minutes and 55 seconds?

Ch5) The Umbral eras have always gone before the Astra eras. Are you getting caught up on the fact that both Astral and Umbral are always labeled with the same number? It goes U1, A1, U2, A2, etc. We're currently in the sixth Astral era. Prior to this was the sixth Umbral era, as indicated in the book. It makes sense that following U6 > A6 would come U7. I'm not aware of any cycle to reference that goes Astral Element, Umbral Element, Astral, etc. so there's no reason why the 6th Umbral can't be Water.