I would move them in early summer, when the leaves start to die down. They may sulk for a year anyway, but they will come back.

Lifted and pulled apart while dormant in summer they shouldn't care a bit. You could even dig them in bloom and it shouldn't matter, as they don't seem to have rooted out for the year yet even at that time.

At least ones bought flowering in retail displays have no roots yet. In the meantime you can probably cut the hydrangea branches back or off right where the bulbs are without it ruining the shrub.

I agree about moving them in bloom. My three sizeable clumps all come from 2 or 3 bulbs that had bloomed in the store. In Holland they were often sold as "dry bloomers": you bought them in late summer or early fall, put the bulb on the window sill to see it bloom there as a curiosity, then you planted them in the garden.

Here I moved mine once they started going dormant in June, but some skipped blooming a year, to my great surprise actually. I did not think they would mind, and not all did.