(Almost) Null Avg Visit Duration

[Merlino1959]

Description
Hi, we've got a number of sites in our self-hosted OWA setup. One (and only one) of them constantly reports "0.00.01" as Avg. Visit Duration on Dashboard page (counting 37,269 page views in the current month), as you can see in the first screen capture. Any clue?

Additional question: is there any way to have the graph reflecting the date range setting? I find it stuck to the first 10 (monitored) days of the set range, or to the last 8 days when entering the Dashboard screen coming from the Reporting screen. No way to show it like GA does?

Example

Thanks a lot