You cannot overdraw your account because your computers clock is wrong.
You cannot overdraw your account because there is an issue with a credit card terminal around clock sync.
This simply cannot happen.
If it can, let me suggest that whoever is writing the account debit code wrap the balance check and debit in a transaction.
You can easily stick a rackmount atomic clock in your data center.
NTP can source from a variety of sources. There are digital RADIO time signals.
On a given exchange, again, you can still trade stocks. Folks forget that there used to be open outcry trading. Even without that an order book can be operated successfully without GPS.
Credit card terminals do not require clock sync with GPS links, they do not have GPS antennas in most cases. If they need precise time, they can timestamp when going through authorization steps to approve the transaction.
It's weird, as someone I guess older, the new generation seems to build such fragile system and think only such ultra complex systems are usable. Yes, things like Google's Spanner are cool. Yes, performance would degrade without GPS (maybe - I can think of some work arounds). But not everyone needs globally distributed consistent databases. You'd be surprised at how much of banking, stock exchange work does NOT depend on anything like these tools.
I wish the HN comments would focus on the many pretty obvious options one could deploy if GPS went away if you even believed that the current system means your bank account will be overdrawn because of a lack of GPS.