Hi Linfo Go,
Thanks for reaching out, allow me to clarify this. Changing this in your file's Settings (by accessing Settings > Account and Settings > Sales) will update it for all new customers created after you have made the change. It does not update the settings for existing customers on the file - this is not available at this time and you would need to update this for the individual customer by following the steps:
Navigate to Sales > Customers.
Select your Customer and Edit.
Under Payment and Billing, set the Preferred Delivery Method to Send Later and Save.
-Kass
