No, I remember there were problems with orders not going through for nearly a 24 hour period, and also all of the Warner boxsets were listed as unavailable before the extension but were available after the extension. Whether that was intentional or a computer error I don't know.
Last year, it started June 8 and Nov. 10; due to server problems the fall version was extended to 11/23 from 11/18. So I stand corrected; spring one starts after Memorial Day, fall one is done before Thanksgiving.
My recollection was roughly Memorial Day and Thanksgiving. But they don't ever pre-announce it that I can recall; it just arrives and then you can't get onto the website until 2 AM.