As a rule of thumb, you can plant when you can buy but a good local nursery can give you more specifics as to possible amendment needs, best plants for your level of expertise and growing conditions.

If bare root, you can plant immediately.

You should not buy growing potted roses in your area until mid May. Most of them have been started in greenhouses or grown in warmer areas and trucked here. They have not been acclimated to this area. After mid May, there should be no problem.