With the new version, godrays creation is really simple, you just have to focus on the sun intensity and the ground fog density. Put any object in your scene, rotate the sun to be behind the object, that's it ! adjust the ground fog density and the sun intensity to increase or decrease the effect.

When workig with volumes, render time can be verry long. To speed up things in cycles, adjust the volume steps ! the default value of 1024 is quite to high, for the clouds to render correctly, 64 steps of 0.1 is fast and fine.

Specially when working with the preetham sky model, the render may look very bright when the sun is at zenith. i recommend to tweak the exposure and to use the standard color space with medium high contrasts , not the filmic one. The preetham model already have a built-in tonemap and render better with the standard color space.

Only the preetham sky model is compatible with eevee, be sure to stick on this one. And you also need to deactivate manually the SKYSIM_scatteringlight object (it is the godrays source for cycles but eevee can produce godrays from sun lamps when cycles can't, so you don't need it with Eevee). I'll try to make that automatic in future releases.

If you're using Blender 2.82 tou can use the integrated sun position plugin. Just select the SKYSIM_Sun in the sun field and your sky will be driven by the plugin. you can create any keyframes you want, the plugin is computing the position on each frame for you.