Single Page App - Accurate first render marker

Has anybody got any good techniques for getting an accurate first render measure in a large production SPA?
We’re using a combination of backbone and react to render the page views…

I’ve tried this technique:
http://www.stevesouders.com/blog/2015/05/12/hero-image-custom-metrics/

It works, and I have events firing, but it does not seem very accurate.

I was wondering if anyone has used a good backbone solution? Basically need to fire an event when render() has finished…

Thanks