PHP Imporrt from XML File to WordPress Site Updated

I have a script which does the following: 1) Opens and reads an XML file 2) Connects to Wordpress via XMLRPC 3) Converts each item in the XML file to a Wordpress Post and publishes it The Wordpress site has over 70,000 posts, each XML file can have up to 200 posts, I need the script amended so that it processes 20 posts, pauses, then does the next 20 posts etc. or it pauses between creating each post. The reason for this is it's currently maxing out the server each time it runs for five minutes.