Hi,
Basically the EPCM.doNavigate takes the navigation target, translate it to a URL then performs a form submit to the content area iFrame.
you would like to recognize when the content is loaded in the content area?
try listening to the onload event of the iframe of the contentArea - then you can display an animation on top of screen.
Please note that portal (at least some apps, mainly WD) have already a loading animation.
BR,
Tal