Magnolia are best pruned after they have flowered in late spring if they really need pruning. If you do it now you will cut the flower buds off. They should not really need it unless it is to give it some shape. Red Robin is best pruned early spring just before it begind to grow again. That way you will get nice fresh red tips developing. You can prune again during the growing season but best not pruned now. As for the Prunus, depends on which type you have. If evergreen then prune early spring, if an early spring flowering tree type then prune after flowering.