Basically we use **custom options** to add two options on the product pages:
- immediate delivery
- delayed delivery
The first option should track inventory (check how much quantity is left in the inventory and decrease the quantity when ordered) and that the second one has unlimited quantity (no inventory and don't decrease quantity).
Magento doesn't allow to do that out of the box.
I would like someone to develop a solution for this specific situation (first option check inventory, second option doesn't).
I can give more details and explanations if needed.