I am not sure about the CO web site, but many sites do a CC verification transaction as part of the process to make sure the card is good and that the charge will not exceed your limit. That is an interactive transaction with the CC company that takes place in a second or 2.

The ending of the transaction executes the ticketing process and has several components including CC charge, ticket issuance (which could be with an e-ticket database that exists somewhere else), as well as confirmation of all segments with the operating carrier. So if the itinerary has codeshare segments, this part of the transaction could take a little time as well, since the codeshare partner creates a PNR in their system and sends a record locator back to CO.