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Filtering google searches by time periods has been one of the most frequently requested features. By manipulating the search url, you can trigger google's filter by data dropdown box to appear. With this drop down box, you can easily select what time dates you want google to filter the results.
do a search on google....for anything
then add &as_qdr=d to the end of the url
Date, usage rights, numeric range, and more
The results appear to be a date range measured back from the present. The feature I'd like to see would exclude recent pages, and give a choice for both ends of the range... probably something that would be extremely difficult for Google to do (and also difficult to define what's actually meant by the date specifications).