The beautiful secret of melt in your mouth chocolate is cocoa butter. The cocoa bean is generally made up of about 50% cocoa butter.
When you warm cocoa butter it becomes soft. Using cacao butter when you are using The Chocolate Refiner is helpful when you make bean-to-bar chocolate.You do not a pre-grinder for your nibs. Most people, including myself, start the machine with nibs. There are are some things that help out when you are starting with nibs:
The warmth of the stones, nibs and other ingredients will speed up how quickly the ingredients refine. Adding the nibs slowly will allow them to refine more efficiently.
The top spring on the machine can be screwed down (never beyond finger tight) to create more tension on the wheels that will impact how quickly the ingredients refine. Initially, having less tension is helpful to let the wheels move freely while the nibs are being added. As the nib size reduces the tension can increase.
Some people are very happy with the texture after 24 hours, some people like it to run longer. Certain beans are more acidic and other flavor components will mellow the longer you run the machine (especially if you don't have the lid on the machine). For this reason, some people may run the machine up to 3 days.