Donn,
I have never 'personally' recieved grasses shipped bare-root but I did work at a grass nursery & 'sometimes' our stock arrived this way.

In my opinion the best time of the year for both warm & cool season grasses would be early spring when the roots are actively growing & when there is little to no top growth. You 'might' be able to do it later with some cool season grasses but you would definitly have to give them a haircut first!

The trick is to keep the roots moist the whole time. I have seen damp newspaper & damp spagnum moss used to varying degrees of success. There is a great product out there that coats the roots with a layer of moist gel. It works very well! Sorry I don't know the name. It comes in a white powder - a bit like fine sugar. You add water and voila!
I will be VERY interested to hear other experiences with these shipping methods.

btw, I'm guessing that this method works much better for small divisions. It is very hard to get the soil back 'into' a large root mass ~ there would be too many voids left over for the grass to survive well.