Unless otherwise agreed:

(a) Payment is due at the time and place at which the buyer is to receive the goods even though the place of shipment is the place of delivery; and

(b) If the seller is authorized to send the goods he may ship them under reservation, and may tender the documents of title, but the buyer may inspect the goods after their arrival before payment is due unless such inspection is inconsistent with the terms of the contract (Code Section 11-2-513); and

(c) If delivery is authorized and made by way of documents of title otherwise than by subsection (b) of this Code section then payment is due at the time and place at which the buyer is to receive the documents regardless of where the goods are to be received; and

(d) Where the seller is required or authorized to ship the goods on credit the credit period runs from the time of shipment but postdating the invoice or delaying its dispatch will correspondingly delay the starting of the credit period.