How Long Should a Full Computer Scan Take?

I've had my full computer scan running for about three hours now. It's at about 45%. Does that seem a little long?

Hello Matt,
I regret for the inconvenience caused. Please confirm whether you are running first virus scan after installing AVG Internet Security in your PC. If so, I would like to inform you that the first virus scan of AVG Internet Security will normally take some time to complete.
Thank you.