I can see how beneficial this could be for you since your business has thousands of customers. However, there isn't a way to import only customer's payment terms into QuickBooks Online. We can import the customer's name and contact information but not detailed information like payment terms.
I recommend looking over these two guides for additional details about importing data into QBO:
Hello, thank you for your response. Your example looks like something we could use, but it won't be including actual orders like yours appears to have. How do we import a variation of your example spreadsheet into QuickBooks online advanced? We will do it either when we import our customers for the first time, or after the customers are already existing in QuickBooks, whatever works best to get our customers' payment terms set up without having to enter them manually for the thousands of customers that we have.