The primary driver of lead time for purchasing suggestions is the lead time of the part on the item master (Part). That can be overridden by a value in Supplier Price List, that is the only place I am aware of that will replace the lead time of a part that is set up through item master.
The same goes for subcontract operation lead times. Whatever is in the part master will be overwritten by supplier price list when MRP creates the unfirm jobs.
When you think about it, this makes sense, as it gives the ability to change an item lead time without having to involve engineering.