I need to dig up and move my butterfly bush when is the best time and should I prune first?
The best time to do this is to wait until spring. They will do best transplanted then. When I worked for a nursery several years ago, we used to trim the tops back pretty hard, then cut off the bottom 1/3 of the roots. This will help it to recover, and come back bigger.
Here is an article that will give you more information: https://www.gardeningknowhow.com/ornamental/shrubs/butterfly-bush/tips-for-transplanting-a-butterfly-bush.htm