Try using UPS some time. 5-7 BUSINESS days cross country. That's up to 9 calendar days and it costs you twice as much.
The Post office rocks.
Delivery times are a function of your local P.O. I live in Tampa, near the airport, which is the major P.O. processing center.
I can get a package to or from a big city in CA. in 3 days flat via 1st class.
If it comes from a smaller town, it takes 2 extra days just to get out of CA.
I can send a package from here and make it to CA in 3 days. Then it sits in some podunk town in CA for 2 days before it makes it to the recipient.
If I ship a package to you from here, it'll be there in 3-4 days. If I ship it from 60 miles South of here, it'll take an extra day or two.
It all depends on how close you live, or the shipper does business, to one of the major processing centers.
If the USPS haters in Congress have their way and shut down more processing centers, you can expect even longer delays.