Your dwarf Owari Satsuma tree does not require pruning to produce fruit. You can prune it to maintain its shape, and to allow light within the tree interior, which encourages the growth of interior fruit. If you are going to prune your tree, do so at the beginning of spring, after all chance of frost has passed for the season. Always remove trimmed branches from the tree’s area, as fallen and decomposing tree material can invite unwanted pests and fungi.