It does depend greatly by program, but I would say that 5 years is VERY optimistic. This data is a little dated at this point, but you can read the NSF years-to-degree study at this link.
http://www.nsf.gov/statistics/infbrief/nsf06312/
You'll see that the national average is 9.6 years, enrolled, for Anthropology. The program I am in basically requires you to finish in 8 due to graduate school policies, so most people here finish around 7.