Is it an automated process, or does the user need to trigger a scan? Both
The background crawler runs every 5 minute. If there is no new article then it goes into hibernation. As soon a new article is added to WordPress, it comes out of hibernation and in the next 5 minutes, it will start process workflow (scan the article, break into keyphrases, score the keywords, launch link discovery, run auto rules against it and so on)
But if your wordpress cron is not getting triggered due to low website traffic then the admin can go into setup and trigger a manual scan.