Yes, any time when plants are dormant is a good time to transplant. My hydrangeas go dormant between late November and December so that would when I would move them but, you should do it when yours go to sleep instead. And before your soil freezes. Prior to the usual leaf out time in Spring is also a good time.

Fall is the best time for planting/transplanting. The cool air and warm soil temperatures are the perfect combination for establishment. Another benefits is that the plants will be entering a period of dormancy. Rather than continuing to transfer energy into new foliage and aboveground growth, they will be transferring energy into their roots and storing nutrients for the cool months ahead.

Come September you should be fine, especially in zone 5 (same zone I'm in).