Maybe I can shed some light by sharing my experience with author chats. I've done one but attended several put on by a popular website. They usually select 3 or 4 authors to feature and each author gets around 10-15 minutes to share about their books. The one I did was very well attended by readers and I sold several books from the endeavor.
A note of warning, you must be prepared. I would suggest that you attend several before being featured. This will allow you to get a feel for the pace with which they move. It will also allow you to become familiar with they type of likely questions the readers may ask you so that you can already have answers ready. I already had a short blurb and a couple of short excerpts copy and pasted into my little sticky notes program so I could paste them into the chat quickly. I was able to take full advantage. I have watched authors melt down because they could do nothing but answer questions and they never got to tell about their book. You want to leave the readers wanting more of your book. When you post your blurb and excerpt they are still going to have questions but you are better in control of the information they leave the chat with. Hope this helps some of you.