Ack, you're totally right. I pulled that link from this https://sproutsocial.com/insights/facebook-stats-for-markete..., which makes that stat sound like it's Facebook-specific.

https://www.broadbandsearch.net/blog/average-daily-time-on-s... puts it at 58 minutes, and https://www.nytimes.com/2016/05/06/business/facebook-bends-t... (from 2016) notes that it's 50 minutes (apparently reporting by FB in an earnings report).