As the foliage gets completely yelllow...you can find them and lift and divide then. You will have to keep an eye on them, or the foliage will dry up and die before you realize.
I'd immediately replant.

One tip is to take a picture of them now, while they are blooming or presenting leaves. Once they begin to die down or are totally withered (since we know we can't always dig at the right time), you will still have an idea of what was growing where. That will help you know where to dig as well as where to transplant.