Time on site and bounce rates are interlinked within GA. In Google Analytics, a bounced visitor is defined as someone that lands on the site but does no further activity on the website. In that case, the time on site for that user is 0 second. This is because GA calculates time on site by looking at the time of second activity – (minus) the time of first activity. As no second action exists for bounced users the time on site is then essentially 0.
A more accurate way to measure time on site is to use events to track interactions on the site. By default, all events impact bounce rate, which is what happens with scroll tracking events. I consider the scroll as a user activity affecting bounce rate but also giving us a slightly more accurate time on site.
Now that these scroll events have been changed to non-interaction, they no longer impact bounce rate or time on site
