When ever you want to.
They are very hardy.

I am also in MI, moved a couple smaller RoS this last spring. No leaves showing, but they came back fine, one small 2ft, one about 4ft.

If I absolutely had to move them this fall, I would do it as soon as the summer heat breaks and water a lot. Mulch well. Get them growing roots before winter gets here.

I have had good luck with mine in moving, but have seen and heard of RoS not making it thru winter colds. Winters now do seem a bit warmer than in the past, maybe that will help if you move in fall.