Custom Calculated Fields

We manufacture products for customers and we would like to use Quickbooks to help with manufacturing scheduling. In our sales orders we have a Due Date which is the date the customer expects the product to arrive at their business. We also use a custom field called Ship Time which is the number of days we know from experience how many days in transit a product will take from our business to the customer. We would like to add another custom field called Ready Date which would be Due Date minus Ship Time. The Ready Date would be the day the production team manufactures/assembles and ships the customers product. We'd like to generate a report in Quickbooks Enterprise that we could print daily and give to the production manager so she would know what products to manufacture/assemble and ship for the day.

For example, the due date for customer A is 01/15/2020. The ship time is 7 days. The ready date would be 01/08/2020. The ship time varies by the customer's location. An overseas customer may have a ship time of 20 days while a Texas one 2 days.

Quickbooks does not seem to have this kind of spreadsheet functionality in the reports or custom fields. Suggestions and dialog is apprei