If a third party javascript file hangs and takes a while to load, will
jQuery(document).ready(function() {})
have to wait for that to
The 3rd party js file may be blocking, especially if it's in the head tag. Try putting it just before the closing tag.
I think the first answer is incorrect - document.ready doesn't mean that all content has to be loaded, it means that the dom is complete. Otherwise, jquery methods run inside this wouldn't run until all images (for example) were loaded, which is not true.
Edit
It looks like the behaviour is different for scripts, but can be browser specific. There is a good explanation here:
JavaScript: DOM load events, execution sequence, and $(document).ready()