Vista - Windows Defender-Scheduled Scan Time

To do a complete full system virus scan (not Quick Scan) takes many minutes. I have mine on a schedule in Windows Defender. When I look at the History log it indicates the time to complete the task is about one minute. Can someone explain the log’s entry? Why is the time to complete so short?
A screenshot link of the History log is below.

Jerry

MpCmdRun.exe runs scans and updates. Maybe it was checking for definitions update at that time.

Thanks for the feedback. You make an interesting point, but everything I did leading up to scheduling the scan seems to indicate a scan should have taken place. Also, if you can read my screenshot, the information in the text box below indicates my scan was completed satisfactorily, and does not mention definition updates. In addition, when I check Defender’s “Last Scan” screen, it indicates a full system scan was performed at 4:00 a.m.
Usually, when I scan for definition updates, I get a reply that updates are current or I need to update.
Jerry

From that picture we cannot tell the parameters that are being passed for the Defender scan to run. Also, we cannot tell if the task itself (not the scan, the *task* as set up in Task Scheduler) is set to wait upon the completion of the Defender scan or to start the scan and then once the scan starts acknowledge that the scan has *completed* before marking the task successful.

Finally, it could be that, if you have not installed any new programs, everything that it has been scanning for the last so many times is now cached, and since nothing has changed, the scan ends pretty quickly.

Thanks for your comments. I tried a test I should have done before and that was to schedule the full system virus scan and then immediately look at the history log. I did that and this is what I can tell you. First, the full scan took 2 hours to complete. I then checked my history log and it showed similar entries. That is, the Start and Completion times were recorded as being about 1 minute apart, same as before. So, I guess that is how it works.
Other virus programs, such as McAfee, show a log as to how long it takes the scan to run. You would think Defender would have similar logs.
Jerry