Google Analytics showing visitors avg time 0.00 sec ?

I dont understand this stats. I am getting traffic from google search engine but these have Average time on website written as 0.00 sec.

What does this mean. are people really coming to my site or not ?
if they do atleast it will take 1 sec for them to close my site
but it shows up as 0 sec

traffic from other sources do have avg site time

 

Anybody have any idea ?

 

I got some of the same stat as you, 0.00 sec.
But others are not.

I'm guessing the visitors came in and went out before the google analytics can start counting their presence time.
Just a wild guess...