My understanding - it should be Lead Time.

Lead time normally means the length of time from the moment the customer places an order to the moment it is received by the customer. It is basically the period of time that customer has to wait for the arrival of the goods or services he or she ordered.

Turnaround time on the other hand is more from the seller’s perspective. It generally means the length of time from the receipt of an order to the completion or shipment of an order.

Delivery time should not be used here.

I think you should write more details or even give an example in your contract to avoid any confusions.