How long does it take standard US mail to travel from San Mateo to Sacramento?

The USPS claims that standard First Class mail will take 3 days to deliver from any point in the US to any other point, no matter how far or near they are. So San Mateo to Sacramento, San Mateo to Redwood City, San Mateo to San Mateo, or San Mateo to Washington D.C. should all take the same time: 3 days.