Well, the mean could be affected by people not finding what they want and moving on to another site, so a high mean time could be a good thing.
I would expect that a good user experience would be reflected in a lower median time spent on the site though, but my knowledge of people's porn habits is admittedly limited.
40% higher is not a very big number either when you consider how low the visitor count is at this point. And time on site could be an important metric, but really it depends why time on site is higher and how that fits into their revenue model or engagement over time (repeat visitors, etc.).
I would expect that a good user experience would be reflected in a lower median time spent on the site though, but my knowledge of people's porn habits is admittedly limited.