Very easy in use and extremely cheap (I'm about memory) animated realtime world shader without any volumetric (all clouds - it's only background, doesn't affect to scene, it's just a fake volumetric animated HDRi)

If you good enough in nodes you can easily replace the "SkyTexture" by your custom HDRi, to add the clouds

You can tune any day/night time, also don't forget to tweak brightness after that