specific demographic information

I am trying to get some very specific info to assess lunch traffic flow. Does any body know of the best way or a website to help me figure out number of people with in a 3-5 mile radius during day time hours and people @ night within same radius?
Thanks for any insight.

melissadata.com has some good free look ups- or you can buy a 1 day pass for pretty cheap. To buy lists I like fastlist.com- consider targeting- carrier route mailings can be wasteful.