Need a tracking PHP Script – “how long people stay on the website?”

[jackwebso]

I want to know, is there a way to track how long anyone has been logged into website and then insert it up for each time they have logged on.

In case, user a logs in for 30 minutes, then later comes back and logs in for an hour, then later comes back and logs in for 50 minutes,

Add it up equal 2 hours 20 minutes. Is this possible?

Thanks