2. Does the amount of time visitors spend on your site affect SEO?
Check this out from Sean at SEO Hacker in his post The World Above the Fold: How it all affects SEO:
If there are 1,000 visitors who click-through to your page and stay there for less than 10 seconds, the search engines will see that and say "Perhaps this page isn’t really that interesting or relevant. Let’s put it a little lower."
I recommend a small header (150px or less), a simple sidebar (or none at all) and content that grabs attention immediately.