There are a couple of options. One would be to use a relative date filter, this can give the option to show the last 6 weeks. http://onlinehelp.tableausoftware.com/current/pro/online/en-us/filtering_add_dragfields_dates_relative.html
Another option is to choose Month/Year when the date field is placed on the filter shelf. Then, select only the desired date, January 2013.
Hope this helps!