I'm adding breadcrumb structured data in my site. Google Webmaster Tools already detect with no error and 6 months gone. But this is not preview on google search.
Search result on Google:
Why breadcrumb doesn't appear on search result?
In short, Google don't guarantee Rich Snippets will be shown even if correctly coded.
Google does not guarantee that Rich Snippets will show up for search results from a particular site even if structured data is marked up and can be extracted successfully according to the testing tool.
Make sure you have implemented structured data properly. for this check with Google Structured data testing tool.
and also make sure you categorized your site properly.
I personally did that on many sites and it works well start shown in some weeks. even on new sites.
have you publish the new post or content after apply codes...? because sometimes results can easily found on latest published content.
also, resubmit your site to google. and give some more backlinks to increase crawl level and speed. You can check your crawling and indexing stats in Webmaster Console.