Tracing a wiki-walk through your links (great stuff!) I wonder if DP is almost as much Remodernist as Pop Surreal. I agree on the "Postmodern techn. and sensibilities". In fact, I keep seeing the various retro-futurist/hyphen-punk movements as in some ways incorporating (paradoxically) both Postmodern and Remodern sensibilities, sort of along the lines of that Dada-Futurism reconciliation line I was pondering in the manifesto post.
On the timeline I'd keep it as a more vague "Interbellum into the early atomic age" rather than set dates. Arbitrary dates always seem so, well ,arbitrary. Eras, IMHO, tend to blend into each other. I'd go as far as to place some 60's things as skirting DP(Rat Pack, etc.).