I just checked the Brooklyn Botannical Garden site...
Once the new growth of sedum is up, to prevent later flopping give them a cutback once or twice in May or June. New foliage will regenerate in a few weeks. Shouldn't be much, if any, delay in blooming - VA has a long growing season.

You can also propagate the sedums from your cuttings, too. With a 6" cutting off the top of a sedum, strip off the lower leaves, and cut the remaining leaves in half and plop in the ground. Must be even easier than that to propagate since I've gotten a couple of volunteers from just unnoticed broken leaves sitting on the soil.

Thanks very much for your quick reply. I'll check out the Brooklyn Botanical site myself. I'm supposing they will bloom okay after the trimming otherwise they wouldn't suggest it. Thanks again.

I am in PA zone 5 and cut back all my sedums by half a week ago. I do it by the end of May every year. Bloom time doesn't seem to be affected by more than a week or so if at all. Keeps them shorter with no flopping. You will have 2 new branches come out of each cut end resulting in slightly smaller flower heads but twice as many as you would have had if you did not cut them.

Thanks to you both. I'll trim them back this week and maybe try propagating them too as suggested. They're about 10-12" high right now.