That's a question you should probably ask them. I'd be shocked if they offer 2 - 3 day priority this time of year, since as far as I know there arent any heat packs that last that long and one of those space-age thermoses that keep almost all the heat would probably cost more than overnighting it.
If you're wanting to have them overnight it then I would think it'll be fine with a heatpack or two and styrofoam. Besides, they have an "arrive alive" guarantee on most items as far as I know.