By default invoice payment terms are the number of days set at your Organization level via the Payment Terms records.
You can create as many Payment Terms as desired, and one set as the Default. This default term will be applied to all Invoices created in the future
Go to your management screen
Locate Manage Payment Terms in the left.
Add all desired Terms. Check the Default option for the Term that should be applied by all default
Important: set a numeric value in the Term (Days) field (even zero is valid) as that value is added to the Delivery Date to calculate the Due Date.