Rancher, to be very safe as far as temps go, I would say that when your extended forecast shows the low temps above 30 around delivery time would be best. I have shipped eggs when temps were much colder than that and they have done quite well, but that assumes they are not left sitting on a loading dock half a day, or delivered to sit on your front porch all day even if they are marked to be held at the PO. Anything can happen, but generally I think cold is better than extreme heat. I use pine shavings in the outer box and that gives them some degree of insulation. Generally mail keeps moving and they would have to sit in subfreezing temps for a long time before the eggs themselves would freeze, but I understand your wanting to wait until conditions are more favorable. Just watch your weather and shoot me a PM about a week before you are wanting to set : )