You can do it any time providing you water the transplants thoroughly and don't allow them to dry up. Just part the foliage with your hands around the edges of the plant and look for a place where there seems to be a bit of plant beginning to set off on its own. Make sure it has its own roots and then dig it out and cut off from the parent.
Alternatively dig up the whole plant and cut or pull it into two or more parts ensuring each section has roots.

Hi, A hanging geranium basket that I divided yesterday looks very limp and ill. I'm not sure what I did wrong. I am hoping to fix my mistake before the plants die completely.

Here is what I did: I purchased a very large hanging geranium basket to be separated for use in my window box. I brought it home, untangled the plant and gently pulled apart the roots of the three plans. I planted them in the window box and watered well. It rained after I planted. I blotted the blooms and flowers with paper towels.

Today all of the blooms are laying flat and the leaves are limp and soft. Is there any hope?

Anytime you divide a plant, water it first. And always, divide a plant not in bright sunlight---do it always in early morning, late afternoon hours, during an overcast, or wen rain is expected.
Get it into the soil as quickly as possible, water it well to drainage and don't feed it until it begins to produce new leaves.

I have a hardy geranium Rosann and I want to know if I can dig it up and move it to another place?