How and when can pot planted calla lilies be transplanted to the outdoors?

I bought my boss a lovely yellow calla lily plant. I think that she can plant it outside eventually, but I have no idea how or when. I did a little bit of poking online, but saw conflicting information.

We are in NE Ohio, hardiness zone 6 according to the internet, but close to zone 5.

Can you help us with some specific directions regarding when and how to move this plant from its pot into her garden? Thank you!