First, Google Analytics reporting does not, to my knowledge, influence SERP rankings. Altering the data collected through Google Analytics should not affect SEO indicators.

Second, this is from here: http://briancray.com/posts/time-on-site-bounce-rate-get-the-real-numbers-in-google-analytics/

Once this code is installed, your site will update Google Analytics every 10 seconds under the Event Category "Time", the Event Action "Log", and the Event Value will be based on the pattern of 0:10, 0:20, 0:30, 0:40, 0:50, 1:00, 1:10, etc.

The script does not change your bounce rate, it just gives you additional information.