Guys - in the USA you don't gain much (if any) time shipping priority mail.
A package shipped today from Delaware to Las Vegas estimated delivery is April 1 for Priority and April 2 first class - my bet would be April 2 for both. Having watched this carefully (with a few exceptions) I ship everything under 13 ounces First Class. It travels on the same airplanes or trucks.
USUALLY, you are absolutely correct. Recently, we have had a couple that took 8 days to Texas via First Class. That is what motivated me to ask.
Of course, the Postal Service SAYS 3 days for Priority and, like you, our experience says that is about accurate.
Also on tracking numbers: Once a package leaves O'Hare for international delivery, the tracking number will only show when it left the USA. So, for international---YOUR country determines when or IF you get the package. The USPS does no good in these situations. BTDT!!