RE: Customer Versus Item Lead Time
The Customer Card doesn't have a Lead Time Calculation field. It has a Shipping Time field. Is this a custom field that was added to your environment?
If you're thinking of the Vendor Card, which does have a Lead Time Calculation field, here is the priority the system uses:
1. Item/Vendor Catalog
2. Item Card
3. Stockkeeping Unit Card
4. Vendor Card