I, on occasion, will copy of bill to get a head start on entering a similar bill. Often, but not always, the bill will have an incorrect due date. The terms are correct.
For example, the bill originally would have been February 10th, terms net 30, but the copied version will revert to net 10 days. Unless I change the date, the inconsistency between the terms and due date will not resolve.
It could be the Company preferences in Bills section was set up on 10 days due. That is why the copied version will revert to net 10 days even the original bill is set on terms net 30.
To prevent this from reverting, let's set the Bill Preferences into 30 days instead of 10.
1. Click the Edit menu at the top.
2. Select Preferences.
3. Hit the Bills section at left panel.
4. Go to Company Preferences.
5. Change the Bills are due in to 30 days after receipt.
6. Click the OK button.
After entering bill in QBDT, please check this article on how you can use the Pay Bills feature to settle your payables for different vendors: Pay bills in QuickBooks Desktop. This article also provides on how to apply the corresponding discount or credit for each payment you make.
Please know that you're always welcome to post if you have other questions related with QuickBooks. I'm always here to help you.