I think it depends on the plant. Some plants (especially those that are only marginally hardy) may not do well if transplanted in fall. Others might benefit from being transplanted earlier. Significant root growth can occur over the winter, so rootballs will have to be larger the longer you wait. If it were me, I might even be tempted to move them now and just be sure to water them well through summer. So, I guess the answer to your question is "it depends".

Thanks Brandon. That is something to think about. Maybe I could transfer the spring blooming ones in the fall, and the fall blooming next spring? Something like that?

I really am so tempted to do it now! But: a) the bed is not ready, and I'm not even 100% sure exactly where it goes. I'm also pondering whether or not I would like to do a raised bed. And b) I told my husband no more beds this year, and he will kill or divorce me if I even look like I am thinking about it. LOL!