I've divided iris in spring time, in the middle of summer, in the fall. Just about any time but winter.
When I've divided them during the hot months, I cut the foliage back by half. I make a raised moundm spread the roots downward and cover only the roots not the tuber. Then I water.
Agree with the other Arkansas gardener that autumn is probably the best time, but mine have done just fine regardless.
Q
Z7/7b