By default when you click on "search options" and limit a search to the last day, the qdr appears as "d." Change that to "n" and you'll be limited to results from the last minute, to "n10" and you'll see results discovered in the last 10 minutes - or "s30" to see results from the last 30 seconds. It couldn't be simpler.
http://blog.omgili.com/?p=108