If the state of Indiana decides this year to change when they set their clocks forward and back, and you stored your appointment datetime as a timestamp, when do you show up for an appointment? At the new 930 AM after statutory date adjustment, or the now incorrect time stamp in your database? Will the DMV respect your claim that you had an appointment at epoch timestamp 1726651800, or will they say sorry buddy the clock on the wall says 9:30 AM, you missed your window? Are your taxes next year due at 1713173400, or are they due at midnight April 15th?
This is NOT a UI issue. This is an issue where the timestamp you calculated in the past literally does not mean the same calendar date in the future as it does now.
And if your answer is to recalculate the timestamp based on locale changes, what was the point of storing the timestamp? (I hope you stored an audit trail of the locale as well as the timestamp, otherwise you can't even recompute the timestamp). The timestamp is never the ground truth, the human readable string is the ground truth.
The timestamp for a particular human date time is not generally a computable function, because human governments change how dates are reckoned frequently, and the human government, not your database are the ground truth.