Which estimated delivery date is correct?

For years I’ve noticed this but just went about my business. But have since been doing some math and sorta wondering what the buyer actually sees on their end when it comes to estimated delivery date? I attached two screenshots. Both are for the same order. As you can see, one screenshot with the order shows one estimated delivery date and the other shows an extra day. Which one is correct? This is for all orders, I always see a deliver by for example “December 20-23rd” on the full invoice and then also just a deliver by “December 24th” which is a day later than the other listed deliver by date. I’m sure I’m not the only one seeing these two different deliver by dates, so can someone please chime in and tell me which one is accurate? If you do the math for processing plus shipping times the later date is correct but then why does one part of the invoice missing one day? I’ve always just followed the shorter date but I’d like to know if that extra day is actually mine to use? Screenshot number one shows the dates listed on the invoice. Screenshot two shows the date when viewing from messages.