Purchase Lead Time

Assuming that you would like to keep the buffer days between the incoming shipment and Delivery Order, to cope with any transport delays, it can be set globally for all the Purchase Orders for the company. Go to Purchase | Configuration | Settings, set 1 as the buffer day in the field Purchase Lead Time *.

Now the Purchase Order date will be computed as follows:

    Purchase Order Date = Delivery Date - (Vendor lead 
    time + 
     Purchase Lead Time)      Schedule Date = Delivery Date - Purchase Lead Time 

So, now your Purchase Order date is July 17 instead of July 18, but the delivery date is still the July 24.