As you are seeing from the responses, it depends...
If they are still dormant you don't need to pot them right away, if you don't think that will work for you. You just need to keep them cold, and make sure their roots don't dry out. If they are still dormant, because they don't have foliage, they don't need any light, so you keep them in a refrigerator or dark cold shed.
If the buds are showing signs of breaking, or if they already have foliage on them, you will need to pot them and protect them from freezing. By "protect" I mean neither the branches or the roots can be exposed to frost or near-frost temps. So nothing 40 or below. Once they start to leaf out, you have to provide them with light, so no dark garages or garden sheds. I don't know how many seedlings you have, but there would be no risk to potting the seedlings and keeping them in your house in a bright window until spring arrives and you can move them outdoors. Because of where I live, there is no such thing as frost risk, so I pot everything the moment I receive it.
At the risk of being repetitive, let me explain it a slightly different way. Trees enter dormancy slowly, and they come out of dormancy slowly. This annual process is non-reversible - once they come out of dormancy, they can't be put back into dormancy by exposing them to cold weather. So if any dormant tree is showing signs of leaves, you have to give that tree a spring, or risk losing it. Trees that are normally very cold hardy can die if exposed to cold weather too quickly in the fall (before they have gone through the process to become dormant), or cold weather too late in the spring (after they have started to come out of dormancy). So if you have seedlings that are still dormant, you can keep them cold and (watching them carefully) hope they stay dormant. But the moment they show signs of waking, you have to give them light and get them into the dirt.