You want to have some people visit your landing page for 5 seconds to see what they take away from it. The point is to gauge the reaction of a typical web visitor that's going to spend less than 5 seconds evaluating your landing page.

There are three services that make this easy.

• fivesecondtest - Just upload a picture and get survey responses about the first impressions quickly.
• FeedbackArmy - You can just link your URL and get feedback.
  
• UserTesting - Get a video review of your page after the 5 second test.