I prefer to get them back in the ground immediately. I know one hybridizer who treats the plants with Banrot before replanting them, but that stuff is way too expensive for me.

Although I don't recommend dividing or planting during the summer, if you are going to do it, it would be a good idea to let the cuts callous over before re-planting.
It would be safer if you are potting them up in a fairly sterile potting medium, then transplanting to your flower beds after they are growing well.
Cooler temps in spring and fall are much better suited for dividing and transplanting.
Ed

Thanks to both of you for the information. I appreciate it and it has been quite helpful. I will follow your folks advice!

I use powdered sulphur which is much less expensive, in fact it is cheap! Put it in a clean Parmesan cheese shaker and keep it on the garden shelf.

Hi Ed!

I think a lot depends on your climate and the soil. If you are in zone 5, maybe now would be OK. I just don't know. It's been so cool here, Ed, I've tempted to do some "fall chores".

Well, that really doesn't make sense. You have to use the sulphur, not just put it on the shelf!

Shake a bit over the cut crowns and leave them out for a few hours before planting. Try to leave the sulphur on the crown intact as you plant and tamp down the soil.