Snoozeman - I think two hours is about right for pompeii. While it is much larger than I anticipated it isn't huge and all of it is not accessible to tourists.
At the entrance was a cameo factory and we got to shop for about a half hour and watch the cameos being carved. Amazing. I'm not a shopper and usually hate these sort of "opportunities' thrown into a tour but this was really interesting. I think too, we were waiting for our group to be called to enter the site since there were quite a few tour groups there that day.