Likely it pre-authorized for a certain amount (say, $100?) immediately upon plugging in, then captures the actual amount after charging is complete (unplugging).
Really, it's hard for me to understand how this could happen. The superchargers have to have an internet connection to charge cards, and they're likely running a unix variant, and they likely have a scheduled job for synchronizing to an internet time server... probably a daily job.
How much drift can really happen in one day? It's usually not in the minutes... it's usually just a handful of seconds.
Perhaps there's some infrastructure failure that they haven't caught yet (e.g. they host their own time server and somehow those chargers failed to connect to it).
If they made a mistake in the NTP synchronization (firewall, incorrect IP, etc.) they never get a time update and they are just drifting. Any reboot or NTP synchronization tries on locked ports, all of which can cause a drifting. I saw this multiple times even on Windows servers.
But because there is no display, nobody can check it and their IT is not interested in monitoring it. Or they even don't know what is time drifting on the machine.
It looks like their best programers are involved in the car software only.