Ken Burns says:

I like to tell people with our Vietnam film, if I'd made it 10 years after the fall of Saigon, in 1985 America was in a recession. Japan was ascendant; we are talking about everything shifting over to the Pacific Rim Vietnam would be the symbol of our decline. If I'd waited 20 years, to 1995, when America was the lone superpower, were in the middle of what was then the biggest peacetime expansion in the history of the United States. We had just won the First Gulf War with one arm tied behind our back with a coalition of dozens of other countries -- we were in clover. Vietnam would have significance, but would no longer be the symbol of our decline.

You wait 30 years, to 2005: were bogged down in both Afghanistan and Iraq, and comparisons are being made to Vietnam. All of a sudden Vietnam has a new centrality. Nothing about the Vietnam War has changed. It's only we're on a different mountaintop.

One way to think about releases is to just concentrate on quality, and then the work will trend whenever history starts to rhyme again. cf. Galbraith's The Great Crash 1929 and its foreword wherein he notes the sempervirence of the topic and the demand for reprints.

Another is that timing matters, so as to lodge it in people's memories or to enter the public discourse directly. cf. Rehnquist's All Laws But One, or Michael Lewis sniping current affairs. If you have the time and capital to wait, this seems the way to go.

Granted, this is a crowded space; just think of the competition for Christmas songs....