Is it OK to separate rhubarb in the fall?
How important is it to wait until early spring to separate rhubarb plants? What are the consequences of doing it in the fall?
Hennepin County Minnesota rhubarb
Dividing it in the fall means that the plant still has large leaves to feed. They will take energy away for making new roots. Dividing rhubarb now probably will not harm the plants, it may set them back a bit. Try to take as much of the root as possible.