I would wait until fall, after leaf drop. If you don't have a place for them to go into the ground right away, then I would wait to dig them until spring, cutting off the link to the mother plant this fall. Plants in the ground tend, in my experience, to overwinter better than plants in pots, especially in the frozen North, ;-)!

I wouldn't leave them longer than the spring however, or their root system(s) will be too big to dig easily, and it would also be too disruptive to the mother plant.

When I layer a branch of a woody shrub, I explore for roots in the early spring while dormant or just starting to swell. If there are roots, I water it back in and let it reestablish after my disturbance (a few weeks or a month). Then when it is growing nicely in the spring, I cut from the mother but leave it there to grow on for the season. Then I move it in late summer or early fall.

I have been doing a lot of ground layering in the last few years, and I have really had good luck with it. Now I bend down a branch or two every time I plant or move something. All my favorite shrubs have a branch pinned down with a rock.

Thank you Dibbit and Gardenscout!
I won't disturb it til next spring, no reason to rush it
and every reason to wait.