Microsoft Bing is now testing displaying the estimated reading time for some of the search results. Within some search result snippets, Bing is adding "estimated reading time" under the snippet. This can be pulling from some structured data or Bing can be using other methods for this.
This was first spotted, I believe, by @NFG946 on Twitter and also Frank Sandtmann, an SEO consultant, emailed me this screen shot of it in action (you can click to enlarge it):
I might add, I personally do not see this in Microsoft Bing - so maybe it is a test?
Forum discussion at Twitter.