Calculate date in order entity based on data in product entity

Hey community,

I want to do the following: Our company is producing goods based on our customer's goods. Basically a finishing process. This finishing process takes anywhere between 8 and 40 hours. Different processes can be bundled into a kit/package.

So if the customer has a desired shipping date, we need the parts to be finished at least x hours in our facilities before shipping. I want to calculate this date.

My idea is:

1. Generate a custom field in the "product" entity where we put in the time for the process in hours.
2. Calculate the date when the parts need to be here based on the amount of products and the corresponding process times within the "order" entity.
   • Date = DeliveryDate - (Amount of Product 1 * Process Time of Product 1) - (Amount of Product 2 * Process Time of Product 2) + [...]
   • Note: The items in the order can be products and/or packages/kits.

How do I achieve my goal? I somehow need to reach the product field from the order entity as well als the amount of each item and that's where I am lost.