I've moved them after blooming without any trouble.... Or while blooming... Or in the fall :)

i think after blooming is the recommended time of the year though. They don't do much while temps are high so I'd avoid the middle of the summer, but come to think of it I believe I've moved them then as well.

Trying to decide when I can divide and move a section of a very large hellebore, I came upon this thread. Will probably wait until early autumn ... however ... this plant, along with most of a woodland garden, was rescued from a bulldozer mid-summer and made the transition very well. On the plus side, the site received morning sun, afternoon dappled shade, I prepared our very sandy soil well, adding home-made humus, and was conscientious about watering.

Good luck with your transplanting!

Personally I prefer mid spring, right after bloom generally. Gives a longer time to settle in and the plants have a good winter foliage coverage for the next winter.