Not sure which product you're using but with FileLocator Pro you can adjust dates using terms like "today -1 week +2 days", e.g.
filelocatorpro.exe -d "c:\search\folder" -ma "today -1 week" -o "c:\output.txt"
Agent Ransack does not support date adjustments, i.e. you can only use a specific date or the relative values of 'today' and 'now'.
More information on date/time adjustments can be found here: