I am pretty sure that Many Waters comes before A Swiftly Tilting Planet.
In Many Waters, Meg is in college. In A Swiftly Tilting Planet, Meg and Calvin are adults, and I believe the twins are in college.
I found A Swiftly Tilting Planet to be the most fascinating and complex of the Time books. I love the way she shifts back and forth between stories and time frames.
I didn't really care much for A Wind in the Door, though - it just didn't grab me. I think part of it was that I found the plot too unrealistic, from my viewpoint as a biologist.
We (mainly Foamy and I, though Shlomo read some of them) read all of these books, and also L'Engle's intersecting series about The Austins. The Austin series has a separate sequence of event and stories, but some characters move between the series. There are more stories about the Murry family that are not part of the Time Quartet - they take place later chronologically.
Our copy of Many Waters had a genealogy showing how the characters are related and what books they appear in, and I used that as a guide to buy further books of L'Engle's about the Austins and the Murrys. Many are not readily available, and I had to order them.
You can find a complete list of L'Engle's books at her website:
www.madeleinelengle.com/books/ "Does the walker choose the path, or the path the walker?"<i></i>