How long does it take for a first class letter mailed from Texas to get to Denver Colorado?

From the usps.com FAQ section: The estimated delivery time for First-Class Mail® is two to three Postal business days. Since First-Class Mail does not have a tracking system, it does not provide the benefit of a guarantee like our Express Mail® service offers. Without a tracking system affixed toFirst-Class Mail, we are not able to tell you where the item is within the mail stream or when it will be delivered.