Returning changed results only

Was wondering how can we have the api return only new urls for a query
say "search engine".
I would want the newer links indexed only. There is some provision of specifiying dates in julian but im not aware how to do it.
Any body knows how to tackle this one ?

 

also an algo to convert normal mm-dd-yyyy dates to julian would be cool. wanna use in php.. something similar to googlealert.com

 

http://uk2.php.net/mktime, use this along with date() to format the date how you wish.