Fiction: The novel was written in three different rooms of the same house covering one event. It was left to the reader to decide in what order the events happened. I read it over 20 years ago.

[Lee]

I read this when I was in college. I thought the title included "Norman"?

[Lobstergirl, au gratin]

Norman as in a person's name? Or as a period in history?

[Kris]

The Norman Conquests: A Trilogy of Plays by Alan Ayckbourn?

Google search -- site:goodreads.com "fiction" "three different rooms" -- lead to this book:

Of Treasons Born by J.L. Doty where a reviewer commented: "Can I connect this treatment of the storyline to that of The Norman Conquests by Alan Ayckbourn where the same weekend is viewed in three different rooms?"