English to Italian Law/Patents Law: Contract(s)

In un Master Purchase Agreement "the buyer may change the order until the scheduled delivery date is within the lead time for the goods".
In particolare non capisco "lead time": su proz ho trovato varie (e diverse) proposte di traduzione. Ecco il contesto:

2. ORDERING/RELEASE PROCEDURE:
Buyer will normally authorize the manufacture and shipment of parts through its Supply Management Web Portal.
The Demand Schedule made available through the Supply Management Web Portal (the “Demand Schedule”) or Buyer’s Purchase Order will provide part number and revision level for releases of parts to Buyer.
Order volume posted on the Demand Schedule is not firm and may be changed by Buyer ***until the scheduled delivery date is within the lead time for the goods.***
Deliveries are to be made only in the quantities and at the times specified in the firm portion of the Demand Schedule.
Buyer is not obligated to accept or pay for parts shipped in excess of any quantity specified in the firm Demand Schedule, and any such excess quantities may be returned at Seller’s expense.
If Buyer does not reject the excess quantities and instead accepts such quantities, the price for additional parts shall be adjusted on a pro-rated basis.