The lead times in Odoo is fixed, and do not take into account quantity ordered.   It also do not take into account if the customer lead time on a product is shorter than the total of other lead times (like lead time for purchase or manufacturing + security lead time).  It do not take into account actual purchase orders or manufacturing orders.  

From the set lead times, it only calculate backwards.   So it do not calculate ATP (Available to promise) on a sales order. 

From my point of view, this a weakness in Odoo for supply chain and MRP.  I reality lead times is not fixed, since logistics is always dynamic.

Read about it in Odoo documentation here:

https://www.odoo.com/documentation/18.0/applications/inventory_and_mrp/inventory/warehouses_storage/replenishment/lead_times.html?highlight=lead%20times