Ask HN: How frequently is the search index on hacker news updated?

I was searching for the hn discussion around Zipkin, a google search lead me to

http://news.ycombinator.com/item?id=4077645

However searching for zipkin on hacker news was showing 0 results at least as of Jun 8 9.50am PST.

http://www.hnsearch.com/search#request/all&q=Zipkin