Forum Moderators: LifeinAsia
The average time a unique visitor is different for every website. It really depends on the quality and attractiveness of your content, and your cleverness in keeping visitors longer.
If you want to closely track this info, there are several stats programs you can install on your web server that will do it. I just discovered BBClone and it does a great job showing how long EACH visitor spends on each page they visit, not just the whole site. It's free too!
blue_eagle is right though, pageviews per unique visitor is a better indicator if you're looking to sell advertising, but "time on site" matters too.