gsap.updateRoot()

Normally GSAP handles all of its timing internally using a requestAnimationFrame loop (or falls back to setTimeout() if rAF isn't available), but some game developers requested a way to manually update the root (global) timeline which is exactly what gsap.updateRoot() permits. This is only intended for advanced users. First, you'd need to unhook GSAP's ticker like this:

//unhooks the GSAP ticker
gsap.ticker.remove(gsap.updateRoot);

And then you can update it with your own custom time like:

//sets the root time to 20 seconds manually
gsap.updateRoot(20);