Google has gotten fresher, our advanced search page started showing more useful options for restricting searches by date. The shortest time frame used to be something like three months; now you can look for things that are less than 24 hours old

Here are all the possible values of the as_qdr parameter

d[number] - past number of days (e.g.: d10)
w[number] - past number of weeks
y[number] - past number of years

For example search  within 24hours

http://www.google.com/search?q=webmaster+group&as_qdr=d1

or example search new url of site within 7 days

http://www.google.com/search?q=site:webmastergroup.org&as_qdr=d7

I’m already using and recommend you using it very good