How long does it take for custom fields to be added to new items?
Depending on server activity, it can take from a few seconds to a few minutes for custom fields to appear on new items you create in your BigCommerce store.

Do I need to manually add the custom fields to new items I create in BigCommerce?
No!  That’s the beauty of the Custom Field Populator.  Once you create a new item in your store, wait a few minutes and go back to that item to see all your custom fields added to the item.