You just triggered a deeply repressed memory. I had to write some software that integrated a properly designed logistics database with an improperly designed USPS mail piece tracking feed. What constitutes a proper design? UTC timestamps. USPS, at the time, provided a service that allowed mailers to track their individually serialized mail pieces with an impressive level of granularity. Every sort machine reported its model number and the nature of the event, which is very useful when trying to track the cause of damage - as some models were more aggressive than others (speed, bend radius, etc). Unfortunately they only reported times in the local representation... "No problem" a much younger and happier me said, "they have helpfully included the zipcode that the scan occurred in!"

That was an absolute nightmare. Nonsensical timezone pockets, not necessarily along postal lines, arbitrarily changing at what point they switch to daylight saving time... and yes, areas around reservations were the most common offenders. Oh and you can't just cleanly ingest the data - converting it to UTC on import, because you only find out that they switched after you start seeing time travelling mail pieces in your staging datastore. I don't think I'd ever been more tortured by a problem, only a couple of years before that I had been fighting house to house in Fallujah - and that USPS system integration had me wonder if I'd made a mistake in not renewing my contract.