Macro needed to sort out courier reports

Hi
I can get two reports from my courier service. The first is a a spreadsheet with the shipping date when it is entered onto their system.
The second separate spreadsheet is the delivery report in a broadly similar format which shows the customers details when the items are delivered to their door.
I need to compare the two worksheets and work out the time taken for delivery (find the same customer in both sheets and take the delivered time and date and subtract it from the dispatch time and date). Put the answer in a new column in the delivery spreadsheet with the delivery performance time next to the specific customer. Not all deliveries are tracked and show notifications for example shipments overseas do not always get a delivery notification.
Not every shipped item has a deliver date, as some items get lost or cannot be delivered due to incorrect address etc.

The courier will not produce this information for us, but some of their deliveries, which should be 48 hours, have taken over 14 days.

Attached are short versions of each file.
Any help will be greatly appreciated.
Thank you.