PITTSBURG, Kan. — To ensure your gifts arrive to loved ones by Dec. 24, check your list twice and have them shipped by these deadlines. For the United States Postal Service (USPS), the last day to ship First Class Mail & USPS Ground Advantage is next Wednesday, Dec. 17. The last day to ship Priority Mail is Dec. 18, and the final time to ship Priority Mail Express is Dec. 20.