In my experience it takes between 3 to 4 days for USPS to deliver a letter 1,000 miles away from my location.
Usually if I send a letter to someone 1,000 miles away it arrives either 3 or 4 days later but most times the letter arrives 1,000 miles away within 3 days.
But if you're sending bills off make sure you send it 5 or 7 days before the bill due date to allow time for delays and allow time for the business to post the payment to your bill.
Sometimes it can take a few days after they get the mail to get to your bill and payment and post the payment so send the bill and payment through the mail as far ahead of the due date as you can.
I've always sent the bills and bill payments 7 days before the due date and sometimes sooner to allow the payment to reach the business.