Length of time to complete scan

April, Just a point in passing… An AVG recommendation… Have a look @ this official AVG article (http://avgclick.me/1KQZHBm).
AVG Guru

Sometimes it takes AVG Pro 5 to 10 minutes to complete a full scan, which I have set it to do thrice weekly, and sometimes it takes almost 2 hours.  I have it set to scan at fast speed.  Sometimes when I check it, it has re-set itself to scan at dynamic speed, but even if I re-set it to scan at fast speed, it might take over an hour to complete the scan.   I am not using the computer during scans. 

Why the tremendous difference in the length of time to complete a scan?

April, Just a point in passing… An AVG recommendation… Have a look @ this official AVG article (http://avgclick.me/1KQZHBm).
AVG Guru