Time on site reduced

After installing vBseo the Time on site in analytics has gone down from 11minutes to around 7.5. I would understand that if there was a huge boost in visits, but there isn't.
I only have +1.36% rise in new visits and +1.76% in pageviews. Any ideas/clues why? There wasn't any other change in the site or in the content in this time.

The more search traffic you get, the higher your bounce rate becomes and time on site goes down.

90% of searchers tend to leave after just 1 or 2 page loads when they've either found what they are looking for or not.

Still, 7.5 is huge. I can't break 2 min!

Actually my bounce rate went down 6.50%.. also my google searches are down by 10%. It doesn't really make sense why the time on site would have reduced that much.

Edit: I ll come back with more data, delete this post for now.

Few stats to tell me if we are going on the right track here.. Oct 17, 2010 (day we enabled vbseo) - Nov 4, 2010

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stats removed for privacy issues
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I understand that it needs time, but shouldn't at least the search engine traffic be going up?

A dip in the beginning is expected. You'll need a good 4-8 weeks before anything starts going up for most sites.

Cheers Brian

When you make big changes like installing vbseo. Of cource you start to get more appearing in the SERPS. And First few weeks google test if you do well in this period your SERP position kept or goes even higher. It's all depend on the content and the presantion you have. The quality content make you raise faster.