When reviewing your websites statistics in Google Analytics just be careful when you are reviewing the statistic Average Time On Site from your Dashboard. It’s important to remember that this data can be skewed really easily by a small number of visitors to your website.
It only takes one visitor to leave your site open in their browser while they take a telephone call to increase this stat.
If you see improvements with this statistic drill down deeper in your analytics account and view the report, Time on Site for All Visitors. This report will show the average time on site broken down by day. This will allow you to see if they have been any days where there is any extraordinary user activity on your website.