the scan was going for 2.5 hours before i shut it down. i was running the standard scan.
It would depend on many things. Like what you have for a system(cpu,ram,etc), what other programs you have running while doing the scan, what you are scanning, content, and how much data.
But it does seem rather long. I can do about 5gb in thorough with archives in about 1h 15m with my model T system.
im having it standard search my whole 80gb HD :-\
I answered your other related topic see below, it would probably have been better to have kept them in the one topic.
http://forum.avast.com/index.php?topic=26766.msg218351#msg218351
My scan at most takes 20 mins Damn shortest scanner I found haha