Taken from this website
Do a search, then add this to the end of what you searched for:
&tbs=qdr:X##&tbo=1
The X## portion gets replaced with:
s## for number of seconds you want to narrow your search to, such as s45 for the last 45 seconds, or &tbs=qdr:s45&tbo=1
n## for number of minutes you want to narrow your search to, such as n5 for the last 5 minutes, or &tbs=qdr:n5&tbo=1
h## for number of minutes you want to narrow your search to, such as h2 for the last 2 hours, or &tbs=qdr:h2&tbo=1
That portion gets added to the end of whatever you’ve searched for initially. For example, say you searched for [kanye west] from the Google home page. After doing your search, you’d add the examples above like this:
Past 45 seconds:
http://www.google.com/#&q=kanye+west&tbs=qdr:s45&tbo=1
Past 5 minutes
http://www.google.com/#&q=kanye+west&tbs=qdr:n5&tbo=1
Past 2 hours
http://www.google.com/#&q=kanye+west&tbs=qdr:h2&tbo=1
The time indicates when Google added the material to its index, not necessarily when it was published.