Are you working in php? If so you could possibly format the date inside of the data file. In the DynamicWebCharts > Data > <page name>_data1.php file you should see the date as either the xlabel or yvalue. If your chart is setup like this then you can wrap the date and strtotime functions around the value to format the data like this:
<label><?php echo(date("d-m-Y", strtotime(<your ['XLABEL'] value>))); ?></label>
This would format the date to be in the dd-mm-yyyy format. If you have trouble applying the formatting code I can take a look at it for you if you post back with a copy of this page.