How long does it take for a letter to go from NJ to CO?

Normally, it will take 3 days if it is out of state and 2 days if it is in state. It all depends on the time of year, and weather across the country.

For example, If there is a big storm in the Midwest, it might delay your letter to get to Colorado. Or if it is near a holiday, like Christmas, it might take longer because of the many letters all wanting to be sent at the same time.