I must wonder how these statistics are gathered. Seems the methods and numbers are behind a pay wall, of course. I only found one graph available publicly on ComScore that simply stated a similar statistic as fact.
Are they simply counting log-in time? If you visit Google for a web search, you're essentially logged into Google+. How long does a web search last? 5 seconds? These Google users will, of course, bring down Google+ log-in times.
Are they simply counting time spent at plus.google.com
? You can interact with Google+ from ANY Google website or through Chrome extensions and never have to really visit the site except to make and read new posts.
Are they including mobile engagement? That's a whole other ball game.
We'd like to know details, instead of just a whole lot of he said, she said so it must be true.
I really expect better from Mashable.