I feel the title is a bit baity. Sure, dates add nothing to a culture when they obscure or de-prioritize the content that doesn't have dates. But they aren't suggesting that dates have no value to history at all, just that their history, which is largely undated, should not be lost to their culture.

And it's a valid point: the idea of "everywhen" fits nicely into a relativistic view of time as a dimension. We may not know where it lies, but that doesn't mean it doesn't exist.

A linear sense of history based on dates will leave out dateless knowledge.

A good chunk of my cultural history is undated and lost to time, including European cultural history and women's history. It's great that some people have been keeping time on what they consider to be important, but we lose a massive amount of information when we only accept dated events as history.