Cannabis Grapeseed Oil Infusion from Non-Decarboxylated Plant Matter - When is infusion done?
My Main question is this... At what point is the infusion done?


This would largely depend on your definition of the word "Done". Your own research reveals a number of opinions on how long it takes for this process to reach completion. In any kind of infusion process the results are not linear. You likely get (something like) 70% infusion in 4 hours. Another 4 hours will get you to 80% the next 4 hours to 85%... It's a condition of diminishing returns, that will probably never reach 100% (or 'done'). How much of the cannabinoids are you willing to just throw away because you don't want to wait for them to infuse? At what point is the infused oil "good enough" for you. 


  Is there a difference molecularly that allows grapeseed oil to infuse
  cannabinoids more easily? ... Which is 'better' to use?


What is the 100% saturation point for various oils given various herbs is far to general of question for us to address with any specificity. Even given the herb the variety of oils still leaves us too much to really address. Lastly, when asking for whether A is 'better' than B it helps for you to provide some tangible criteria. I propose that if you want to use it as a salve coconut oil would be better (solid at room temperature) where if you want to cook with it, grapeseed oil may be the 'better' choice (higher smoke point, cleaner flavor).