The KB does not appear to search by tag, but rather by the content of the article?
The knowledge base updates it’s search index every hour and half hour (i.e. 1, 1:30, 2, 2:30 etc).
Tags are indexed, but search is based on the tags, the title, and the content of the article.
There’s a hidden feature, in which if you type “tag:tag_name” in the search field it will take you to a list of articles that are tagged with that tag_name. For example, if you search for “tag:google,” the system will bring you to all articles tagged with “google”