Maybe two or three seconds. If your ad works, the reader might spend another 30 to 60 seconds on your page. If not, you've lost him. Entice people to read on with concepts that are humorous, surprising, exciting, unusual, and relevant. New news is the best news.
Nothing is stronger than a truly new product or service.
If you have any news for your audience, put it in the headline. Let benefits drive your headlines. Make sure your image works with your headline. Don't sacrifice clarity to wit. There isn't time for the reader to figure out puns and word play.