Hello styxblue,
please be informed that AVG is caching trusted files and these are skipped when scanning unless they are changed. After all possible files are cached into local AVG database, the scan performance is significantly better. More information about AVG Cache Server can be found in FAQ 3287.
Thank you.
I am doing a full scan on my computer and it normally takes 30 minutes or so but the last 2 I did only took 2 to 5 minutes. What would cause this?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic