it doesn’t work for me. I pause the video to the image I want, click the “set as preview” button" and 30 minutes later I’m still watching this little circle spinning with no update.
UGH!
New Feature: Choose Your Own Video Thumbnail!
Yesterday tasted this wonderful feature. Cool, now just what I need 
Reply to @steveeyes: It may take up to 24 hours, if I remember correctly. I have a 24 hours shift or even less.