Many grass fanatic growers and many opinions could appear in regards to your question, my opinion and proven results are to split any grass in the spring after new growth has made its appearance.

Jake

Here in CA, I divide in February.
Dig up the clump, place on driveway.
Take shovel. Making sure each piece has adequate roots, cut into as many or few pieces as you would like.
Plant divisions immediately in pots or the ground.
Enjoy.
Ease of digging up and dividing is another reason to love this particular grass.

I would wait until Spring. Calamagrosis is a cool season grass so it will break dormancy way before the warm season ones. When you see the first signs of new growth, dig 'em up and give them the split. They will be none the worse for wear.

Blackie