Uniheat10 Pack 72 Hour Heat Pack - for Baby Chicks, Plants, Fish and Retiles

For those using these to ship plants during winter, are you putting these at the bottom of the pot within the box or how?

How are they for shipping live chicks?

Can you use this product to provide ambient warmth under plant covers for overnight freeze protection?

Description says that it lasts over 20 hours but overview says 72 hrs, which is it?