Vent all you want. Most of us understand.
Some people at the post office are better than others, just like any group of people anywhere. Most will follow procedures and try to take care of the chicks. I wish you luck in getting decent people handling your chicks.
With 26 chicks in that box they should generate enough heat to keep themselves warm as long as the box is not set outside on a shipping dock for any length of time. That’s why most hatcheries have a 25 chick limit this time of year, but that limit may drop to 15 later in the year. They want their chicks to arrive alive and having enough to generate enough heat helps with that. The odds are pretty good they are staying warm enough.
The chicks absorb the yolk before they hatch. They can live off of that yolk for at least three days, often longer. They don’t need to eat or drink for that long. I’ve seen chicks go five days without eating or drinking when I put some incubator chicks under a broody hen. She waited that long before she brought them off the nest to eat and drink. But that was in warmer weather. In colder weather they will use more energy to keep warm, especially without a broody hen, so the limit is probably closer to three days.
Your biggest risk with those snowstorms is that they get delayed in shipping. That’s a risk we take ordering this time of year. You don’t know what the weather will be like when they are shipped. I did that last year and lucked out. It was below freezing when the post office called but they were not delayed in shipping. They were all fine.
All I can suggest is have the brooder ready so when the post office calls you just go get them. Instead of using that nipple water system immediately I’d suggest putting water with electrolytes in a shallow bowl for their first water. If you don’t have electrolytes just use some sugar dissolved in the water. Put some small rocks or marbles in the water so they can walk on top and not drown. Don’t worry about them getting their feet or even body wet, in the warm brooder that won’t matter. Drowning would. Dip their beaks in that water when you first put them in so they know where the water is. After the first day get rid of that bowl and just use regular water and your nipple system. You don’t want the sugar water to go sour. I’ve never used the electrolytes so I’m not sure if they will clog the nipple system or need to be cleaned. The electrolytes or sugar give them instant energy and help them recover from shipping stress.
I wish you luck. Most of the time shipments this time if the year make it just fine, but when the weather hits there can be disasters.