Using Display Actions/Refresh after Service should resolve your issue, as in the following screenshot:
However, your implementation has a major problem. Consider what will happen when 2 users request a chart simultenously ...
One alternate solution to this could be to add the script source to the Tersus welcome page (this is top level page created by Tersus which contains all client-side scripts). and then send the <Body> part of your html to an HTML Display, getting rid of the HTML Tag iframe.
See http://www.tersus.com/#Id=1390, for details on how to customize the welcome page.
For best results, use the Firefox browser..