Not trying to scare you, and memphis is a few hours west of me, but here in middle tn the temps tonight are supposed to get down in the low 20's. If they are being held there overnight I would suggest trying to make sure they are being held inside somewhere safe.
Something else to make note of, the guaranteed delivery time for you depends all on how you are zoned, I used to be by noon, now I'm 4:30. I did not know I had been rezoned until I had an animal inbound to me and realized it was listed as a 4:30 delivery time...I was not a happy person although staying calm and talking with fedex I was able to manage to get delivery earlier.
Best of luck to you guys having animals delivered, I hope they arrive safely.