I am posting two screen shots of my Google Analytics in which Avg. Session Duration is different. Why is that ??
One screenshot is from Landing Page and other is from All Pages tab. I am using a WordPress plugin which shows page by page stats https://wordpress.org/plugins/wp-analytify/ and It is showing that page stats from Landing page.
You're comparing two ways of looking at pages:
Try applying a segment to exclude bounce sessions and you should see your average session time get much closer to the 2 minutes listed in the pages report