Hi Vasily
XML is automatically read each time the map loads. So updating the XML file means that your markers will change in real time on the front end.
Each map has an XML file for the markers located in the wp-content/uploads folder. To switch on XML functionality, go to Maps -> Settings -> Advanced (tab) and select the appropriate option. You also have the option of changing the DIR and URI of where the XML files are loaded from.
To answer your other question, the short answer would be no. I would suggest going with the XML option as this has a delay of 0.
Kind regards
Nick