How do the 30 great years relate to van Hayek and Keynes's philosophies?
I wonder if you are talking about the idea that is contained in The Commanding Heights. Your previous questions seem to be referring to this book/DVD. I don't remember this exact term being used in the book, but the idea is there.
In the book, there is the idea that the US had thirty years or so of boom times after WWII. The fact of this boom would seem to support Keynes's ideas because the US government was being rather interventionist during this time. It was at the end of this time that President Nixon said that everyone was a Keynesian. The fact that the US boomed during such a time would seem to support Keynes's ideas.
However, a conservative could argue that the US was booming in spite of Keynes's ideas. By this argument, the US boomed during this time because of the unique historical circumstances. The US was so far ahead of everyone else after the war that it could pursue bad policies and still thrive in the short term.