I've switched to using Adjusted Bounce Rate by adding the following code to my Google analytics script.
setTimeout("_gaq.push(['_trackEvent', '60_seconds', 'read'])",60000);
The resulting changes in this statistic in my Analytic reports are as expected.
But creating this event has also caused a change in the Avg. Session Duration metric. This number has increased, but not by the full 60 seconds declared in the above code but more on the order of 45 seconds or so.
Could someone please explain to me why that would be.