Express Mail by the USPS (United States Post Office) does deliver 365 days a year -- including weekends, and holidays -- with NO SURCHARGES, FUEL CHARGES, FREE $100 INSURANCE, FREE SIGNATURE CONFIRMATION, and FREE PICK UP. (And if they don't attempt the first delivery within their promised service comminttment, you can get your full payment back for the postage, but you must use a special form you get at the post office.)

Check the exact delivery commitments at this link here before you promise, or expect, overnight shipping.

http://webapps.usps.com/expressmailcommitments/landing.jsp     <<<<  (cut and paste entire link into your browser)

• AND, remember, you must get the package to your local post office or reception BEFORE cut off time.
  If you don't, add a day to the delivery time. 

• You can request FREE pick up, but don't assume your postal carrier will finish his or her route in time to take the package back to the post office in time for the cut off.  In many cases, it can be AFTER the cut off time locally, again, adding one working day to the delivery (excludes Sat./Sun./Holidays in most areas). So your 'overnight' package turns into three or four days.

IF the customer incorrectly assumes 'express' is overnight from the day he or she pays, and it doesn't get delivered the next day, you will have an unhappy customer that paid an exorbitant price to ship.

I hope the above information clarifies, or at least summarizes, the Postal Service Express Mail service.  USP 'red label' might have more exacting delivery commitments, but you might incur Saturday charges for Saturday-authorized deliveries, and they do not delivery 365 days per year like the Post Office claims they do.