Nice set of Google Analytics helper plugins.
Riveted is measuring the amount of time users are actively engaged (e.g., clicking, scrolling, using the keyboard) and then reporting the data to Google Analytics in frequent intervals. GitHub
Scroll Depth is a small Google Analytics plugin that lets you measure how far users are scrolling. GitHub
Screentime is a small tool that helps you start thinking of your website traffic in terms of time instead of hits (pageviews, visits, etc). You can define areas of the page, called Fields, and then Screentime will keep track of how much time each Field is on screen for. GitHub