//1000mls x 60s=60000mls   60000mls x 5m=300000mls
var timer:Timer = new Timer(300000);

timer.addEventListener(TimerEvent.TIMER, llamar);

function llamar(e:Event=null):void {
  var loader:URLLoader = new URLLoader();
  loader.load(new URLRequest("http://www.tudominio.com/dameip.php?user=user&pass=1234"));
}
timer.start();
llamar();