There is a rough gardening rule of thumb that recommends perennials that flower before the end of June be divided in fall and late season flowering perennials are divided in early spring. While this is not a hard and fast rule, it does reinforce the concept that perennials are best divided when not in active growth or flowering. For example, I divide spring ephemerals whenever they begin to go dormant.

End of July/August is not an ideal time to divide anything. But sometimes you just have to do what you have to do! If you are careful about it you should be successful but if possible, I'd wait.

Thank you. I will wait until spring.