Scan Times

Norton Security

I have a question about an odd anomaly. (Log shown is in reverse order)
The following are log summeries from Norton Recent History Log of March 14.

Sunday March 14, 2010 8:16AM User logged into system.
       Advanced Details
                       Catagory Firewall - Activities
                       User logged in
Sunday March 14, 2010 8:35AM Idle Full System Scan results.
       Advanced Details
                       Task Name - Idle Full System Scan
       Scan Time(dhms) 0:01:22:10

My question is. How can a full system scan taking 1 hour 22 minutes 10 seconds
occur if the system has only been running for 19 minutes.
Stats
XP Pro SP3
Norton Internet Security 2010 Version 17.5.0.127