From our experience it takes about two weeks until Google will add the ratings to its search engine results page (SERP). It’s really varies according to your site’s content type & quality, crawling frequency, pagerank, and many other parameters. Moreover, it also depends on the visitor’s country and device, so some users might see it while other’s don’t
Even though we have many clients that the ratings appeared on their SERP, we can’t assure that Google will eventually add the ratings’ Rich-Snippets. Unfortunately we don’t have an access to Google’s algorithms
What we can assure is that we follow the correct meta format schema rules according to Google’s recommended standards and you’ll be able to verify it via Google’s official Rich-Snippets testing tool.