E. , The U.S. Postal system went thru a lot of changes.. Even within country you can not get guaranteed Priority 2nd day mail.... IF, if its pretty close to your state yes. But from NY to CA they can no longer guarantee it will be 2nd day!..... And Customs is its own entity . Both organizations are short handed,,,seems no one wants to be a mailman any longer..
With a new administration in a few years things will probably get a bit better..... - But as long as your customer has their tracking number it will tell them exactly where the package is... One time I waited a month and when I checked where it was it was 5 miles away from me. I took a 3 min drive and picked it up instead of waiting for it to be re routed to my post office!. Have patience guys...