If I have them and they are late, I mail them further south.
If it is above 50, you can release them. They may be able to travel further enough south to find nectar sources. Some have traveled pretty far in one day if the migration weather is good.
I've noticed that those fall migrants seem to eclose with pretty full abdomens. Maybe the fall migrant caterpillar knows that they have to put on a few extra ounces. I know the butterfly is able to put on extra weight. Perhaps, keep a few days and feed it before you release it if you can't mail it further south. Remember, you have to have a permit to mail over state lines.
Herndon, VA (USA)
Take care of the small things....