There are instances where you want to scrape a list of urls for link building but would like to stay relatively current. For instance you scrape forums for your keywords but end up with very old threads that get you instantly band when trying to post. In such cases you want to restrict results either to a the last x months or to a particular date range.
Restrict to last x months
To restrict results to the last x months you put the search operator date:x where x is the number of months to go back. So for instance date:3 in your query returns results indexed within the last 3 months only.
Dates within a range
Its a little trickier to restrict dates to a particular range. Basically you put your date range in normal format at the site and it converts to Julian format. To convert normal dates to julian format there is a tool at http://jwebnet.net/advancedgooglesearch.html#advDate.
You then add this to your advanced search using daterange: operators As an example “keyword daterange:2455928-2456293” returns results of your keyword indexed in 2012 (1/1/12-31/12/12).