They can keep in the fridge for several months. Just watch for any mold. In theory, once the ground is thawed (I assume a non-issue for you) they can be planted. They will just lie there dormant until conditions are right to sprout. However, the danger to this is during this time there is the possiblity of the rhizome rotting, as at this stage (new plant) it is less well able to defend itself. If you've got a great location that is properly drained, you probably won't have a problem. I'd say in general, once it is time to plant peas in you area, you're definitly safe and the rhizomes will probably start growing fairly quickly.