How long for first class letter to get from CA to NY?

depending on where you letter is going it should only take the minimum of 1-3 days.

First Class Mail is delivered in 3 to 5 days.

First Class Mail is delivered in 3 to 5 days.

The USPS will not estimate such delivery time; they state that delivery times "Vary" for First Class Mail.

first class mail is delivered in 3 to 5 days